Summary

Currently, there is no way to search for issues commented on by a given user using JQL; the closest way would be to use "updatedBy", but this includes a significant number of operations alongside comments (creating an issue, updating any of the issue's fields, creating or deleting a comment, or editing a comment).

Suggestion

Add a new JQL function "commentedBy" with the conditions of "updatedBy":

Suggested syntax:

commentedBy(user)
commentedBy(user, dateFrom)
commentedBy(user, dateFrom, dateTo)