I got problems getting text back into the summernote editor.
I already tried (but did not work):
$(\"#EDITsummernote\").innerHtml = \'test\';
         
        Insert Text:
$('#summernote').summernote('editor.insertText', 'hello world');
You can use this line if you want to set (paste) HTML code in editor:
$('#summernote').summernote('editor.pasteHTML', '<b>hello world</b>');
Source code
Bonus
Clear all editor content:
$('#summernote').code("");
None of the Solutions works for me until I did this.
<textarea name="description" class="form-control summernote_rpt summernote_custom"></textarea>
Let's say you have initialized summernote something like this in which I have two classes
.summernote_custom was used 
$('.summernote_rpt').summernote(options); 
when the entire page loads and when I wanted to update the summernote value using js I used
$('.summernote_rpt').summernote('code','data');
$(".summernote").code("your text");
To set:
$('#summernote').summernote('code', '<b> hello world </b>');
To get:
var get_code = $('#summernote').summernote('code');
Documentation: http://summernote.org/getting-started/#get--set-code
Since v0.7.0 code() has been deprecated and removed (same story for destroy() method). 
You must use $(".summernote").summernote("code", "your text");
Reference: https://summernote.org/getting-started/#get--set-code
After v0.7.0, direct jquery methods,
destroyandcodewere removed for avoiding conflict with other jquery libraries. You can call this methods with summernote api.
To set text in the summernote editor:
$('#summernote').summernote('editor.insertText', 'hello world');