The way I usually find where something is coming from is by looking at the rendered source code for text strings that have a good chance of being relatively unique.
I find that id and class attribute values are often helpful for this.
For example if I see
<div id="sp_blurb">
I will use my IDE or text editor’s “find” feature to look through files for the string “sp_blurb”.
Then I look at those files to see if there are any that have HTML mark-up that looks like what the generated HTML looks like.