On Linux, Mac or Windows with Git Bash, open a terminal window. Then run the following command:
ls -la ~/.ssh/
Your public keys will end with '.pub'. you can then run
or similar, to dump your key onscreen. You can then copy/paste it into your SSH key management area.
Windows with Puttygen
When you create a public/private keypair with Puttygen, you specify where you want to save it. This can be anywhere. Typically, though, putty only saves the private key, and regenerates the public component when you load it.
You'll need to open Puttygen, and then find where you saved the key in your documents. If you can't find it, it might be easier to generate a new one.