You are using Qubes with Split-GPG, but you want to verify your GPG key at Keybase.io, via the command-line with bash and curl (you're not storing the key on Keybase's servers).
The verification command is a curl request but includes calls to the gpg command-line client. You have two problems:
1) Your GPG VM is not connected to the network (for good reason)
2) Another VM that is connected to the network, can't use the gpg command.