We Keep Coding

add data- attributes by reading values from DOM

I have the below html structure and I'm trying to get the text of h tags and add as a data- attribute in the corresponding tags:
<div class="content">
<div class="body">
<h1>foo</h1>
<p>para-test1</p>
<p>para-test2</p>
<div class="link">
anchor1
anchor2
anchor3
</div>
</div>
</div>
<div class="content">
<div class="body">
<h1>bar</h1>
<p>para-test3</p>
<div class="link">
anchor4
</div>
</div>
</div>
So 'foo' should be set as a data attribute value for anchor 1,2,3 elements and
'bar' should be set as a data attribute value for anchor 4. Something like this:
<a data-custom="foo" href="#">anchor1</a>
<a data-custom="foo" href="#"">anchor2</a>
<a data-custom="foo" href="#">anchor3</a>
<a data-custom="bar" href="#">anchor4</a>
I tried to iterate over the elements and I'm struck at the second loop.
$(".content .body").each(function() {
$(this).find(".link").attr("data-hN", $(this).next(":header").text());
});

You have an extra double quote two times in your HTML. But, fixing that and foregoing JQuery (which is overkill for such a trivial task), see comments inline below:
// Loop over the links
document.querySelectorAll("div.link > a").forEach(function(item){
// Set the current link data-custom attribute to the nearest
// .body ancestor and the first heading element within that text
item.dataset.custom = item.closest(".body").querySelector(":first-child").textContent;
console.log(item);
});
<div class="content">
<div class="body">
<h1>foo</h1>
<p>para-test1</p>
<p>para-test2</p>
<div class="link">
anchor1
anchor2
anchor3
</div>
</div>
</div>
<div class="content">
<div class="body">
<h1>bar</h1>
<p>para-test3</p>
<div class="link">
anchor4
</div>
</div>
</div>

Can I check with jQuery if element has specific class and edit only this element?

if (jQuery("li.store .premise")[0]) {
jQuery(".address .arrow").remove();
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="store">
<div class="address">
<span class="arrow"></span>
<div class="results-toggle">
<div class="shop-address">
<div class="street-block">
<div class="thoroughfare">demo address</div>
<div class="premise">additional info</div>
</div>
<div class="addressfield-container-inline locality-block country-BG"><span
class="locality">New York</span></div>
<span class="country">USA</span>
</div>
<div class="shop-phone">+1 4258741</div>
</div>
</div>
</div>
Is there a way to check if an element contains specific class and if it does, then to edit only this or these elements.
I have a list of stores and I want if some of them contain specific class to remove the arrows.
I tried with this but it removes all elements with a class arrow and I want to remove the only storeеthat have the specific class which in this case is class="premise"

Closest using get parent element then find class for .arrow then remove method using removed.
$(".store .premise").closest(".address").find('.arrow').remove();

Once you have a collection of premises, use .closest to navigate to their ancestor address, from which you can get to the .arrows:
$('div.store .premise').closest('.address').find('.arrow').remove();
(assuming that the .store element in your actual code is a <li>, otherwise use div.store or just .store)
$('div.store .premise').closest('.address').find('.arrow').remove();
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="store">
<div class="address">
<span class="arrow">arrow here</span>
<div class="results-toggle">
<div class="shop-address">
<div class="street-block">
<div class="thoroughfare">demo address</div>
<div class="premise">additional info</div>
</div>
<div class="addressfield-container-inline locality-block country-BG"><span class="locality">New York</span></div>
<span class="country">USA</span>
</div>
<div class="shop-phone">+1 4258741</div>
</div>
</div>
</div>

Rearranging the order of divs in an RSS using jQuery

I need to rearrange the div order of an RSS. Each item has 3 divs. I will need to move the div with the class "itemDate" before the div with the class "itemTitle" (see markup below). Should I use the function .each(); is there a jQuery out of the box solution for this or do I need to write my own function?
<div id="RSS">
<div class="col-md-3 item">
<div class="itemTitle"></div>
<div class="itemDate"></div>
<div class="itemContent"></div>
</div>
<div class="col-md-3 item">
<div class="itemTitle"></div>
<div class="itemDate"></div>
<div class="itemContent"></div>
</div>
<div class="col-md-3 item">
<div class="itemTitle"></div>
<div class="itemDate"></div>
<div class="itemContent"></div>
</div>
</div>

There is a function in jQuery called prependTo, which moves a element to the beginning of a given target. Check it out the example below.
$('.itemDate').each(function(){
$(this).prependTo($(this).parent());
});
This code just move every itemDate into the beginning of every respective parent.

Toggle a repeated class in jQuery

I have this HTML code:
<div id="content">
<div class="profile_photo">
<img style="float:left;margin-right:7px;" src="http://gravatar.com/avatar/53566ac91a169b353a78b329bdd35c95?s=50&d=identicon" class="profile_img" alt="{username}"/>
</div>
<div class="container" id="status-#">
<div class="message">
<span class="username">{username} Debugr Rocks!
</div>
<div class="info">24-oct-2010, 14:05 GMT · Comment (5) · Flag · Via Twitter
</div>
<div class="comment_container">
<div class="profile_photo">
<img style="float:left;margin-right:7px;" src="http://gravatar.com/avatar/53566ac91a169b353a78b329bdd35c95?s=32&d=identicon" class="profile_img" alt="{username}"/>
</div>
<div class="comment_message">
<span class="username">{username}</span> Debugr Rocks! XD
</div>
<div class="comment_info">24-oct-2010</div>
</div>
</div>
<div class="profile_photo">
<img style="float:left;margin-right:7px;" src="http://gravatar.com/avatar/53566ac91a169b353a78b329bdd35c95?s=50&d=identicon" class="profile_img" alt="{username}"/>
</div>
That is repeated two or more times. What I want to do, is to when I click the "Comments (5)" link, the class "comment_container" appears, but only the one in the same "container" class.
It's this possible?

You can use .closest() to go up to the .container then .find() to look inside it, like this:
$(".toggle_comment").click(function() {
$(this).closest(".container").find(".comment_container").show();
});
You can try it here, if you're curious about finding other things relative to this here's a full list of the Tree Traversal functions.
As an aside, there's an error in your HTML that needs correcting, this:
<span class="username">{username} Debugr Rocks! </div>
Should be:
<span class="username">{username} Debugr Rocks! </span>

jQuery: Wrap only first and second child, not the rest of children

In my actual code:
<div id="mother">
<div id="child-01"></div>
<div id="child-02"></div>
<div id="child-03"></div>
</ul>
I need to produce:
<div id="mother">
<div id="myWrap">
<div id="child-01"></div>
<div id="child-02"></div>
</div>
<div id="child-03"></div>
</ul>
I was playing with wrap, .wrapAll() and children, but I'm stuck.
If in my actual code i have:
<div id="mother">
<div id="child-01"></div>
<div id="child-02"></div>
<div id="child-03"></div>
</ul>
<div id="uncle">
<div id="cousin-01"></div>
<div id="cousin-02"></div>
<div id="cousin-03"></div>
</ul>
How do i produce:
<div id="mother">
<div id="myWrap">
<div id="child-01"></div>
<div id="child-02"></div>
<div id="cousin-02"></div>
</div>
<div id="child-03"></div>
</ul>

First as Adam said remove the # prefix from your id attributes. Also match your closing tags, currently you have a </ul> where a </div> should be.
Then, you can do it using :lt() and .wrapAll() like this:
$("#mother div:lt(2)").wrapAll("<div id='myWrap'></div>");
This gets everything less than index 2 (0 and 1 are the first 2), then wraps it. You can test it here.

Remove # from your HTML ids.
$("#mother div:eq(0), #mother div:eq(1)").wrapAll("<div id='father'></div>")

sharp should not be part of the id's. Then you can do:
$('#child-01, #child-02').wrapAll('<div id="#mywrap" />');

$(document).ready(function(){
$(".new-grid__item:nth-child(1), .new-grid__item:nth-child(2)").wrapAll('<div class="child"></div>');
});