Unless it is specified on the .ssh/config it will use the default private key file.
The default file is ~/.ssh/id_rsa or ~/.ssh/id_dsa or ~/.ssh/identity depending on the protocol version.
Git is using;
ssh/config it will use the default private key file. The default file is ~/. ssh/id_rsa or ~/. ssh/id_dsa or ~/.
You can also grep the standard error output of the ssh command to find the key file like this: ssh -vv user@host 2>; >(grep Offering) - this will make things easier. The last file should be the public key. For example: debug1: Offering RSA public key: /Users/macbookpro/.ssh/id_rsa
