git diff will show you the differences between commits use the below commands
git diff mybranch master -- myfile.cs
git diff mybranch..master -- myfile.cs
In the case of the second command, either side is head it may be omitted.
Master..mybranch will compare master with mybranch
Thus, you can compare the files from two different branches.
For more information please go through the following tutorial to get more info about git: