Can I find out who modified given file last?
Can I also find out a list of changesets which affected a given file?
This command should give you all the commits that changed this file with the diff. You can also see who made this commit.
git log -p <filepath>
I had the same question but found that the previous answers do not limit the output to the person as the OP asked.
Following will show the author with his/her email.
git log -s -n1 --pretty='format:%an %ae%n' <filepath>
see https://git-scm.com/docs/pretty-formats for more format options