After doing a git fetch, do a git log HEAD..origin to show the log entries between your last common commit and the origin branch. To show the diffs, use either git log -p HEAD..origin to show each patch, or git diff HEAD...origin (three dots not two) to show a single diff.
There normally isn't any need to undo a fetch, because doing a fetch only updates the remote branch and none of your branches. If you're not prepared to do a pull and merge in all the remote commits, you can use git cherry-pick to accept only the specific remote commits you want. Later, when you're ready to get everything, a git pull will merge in the rest of the commits.
I'm not entirely sure why you want to avoid the use of git fetch. All git fetch does is update your local copy of a remote branch. This local copy doesn't have anything to do with any of your branches, and it doesn't have anything to do with uncommitted local changes.