This script counts the number of others' posts on which you have edited either the title or body.
Q&A for community managers, administrators, and moderators
Declare @UserId int = ##UserId##
select count(distinct p.Id) as 'Posts Edited'
from PostHistory h, Posts p where
h.UserId=@UserId and p.Id=h.PostId and p.OwnerUserId!=@UserId and
h.PostHistoryTypeId in (4,5)