how to find files with .j or .jp extension

I have some image files that have a messed up extension. The files are of the following format: "filename." "filename.j" "filename.jp"

I need to find all these files which are in several folders and rename all of them to .jpg.

Anyone can show me a quick way to look for all these files? Also once I find them how can I rename all of them to .jpg in batch?