The window title "Question" is not really that appropriate, and confuses more than explains. Better would be for example "Wrap search?"
Dialogs are categorised into errors, warnings and questions, its telling you its not an error or warning, ie nothing is wrong, it just wants to know what to do next. Thats a question.
The string _was_ not found in the part of the document searched so far, maybe it could be `"string" was not found between the start of the search and the end of document`, but then the dialog is getting big and wordy. The find is indeed run "again" from the start of the document.
A standard dialog is used for these questions and "Find" is a stock button. I doubt "wrap" is. If "wrap" is one then its probably fine to change, pull requests are welcome.
"Cancel" is the standard GTK GUI button in accordance with the human interface guidelines for "Cancel the operation and close the dialog". It should not be changed.