But you might have misplaced it, so here's how you can check:
A git repo always has a hidden ".git" folder in it, so you can know if you are in the root of a git repo by the presence of the hidden folder. You can list hidden files using the 'ls -a' command.
(17:05:29 Sat Feb 18 2012 cs61c-td@hive9 Linux x86_64)
~/test/path $ ls -a
. .. .git lab4 proj1 proj2 README
Hence my git repo is in ~/test/path.