If it's second hand, yes.
SonicWall licenses work through MySonicWall.com. I would expect the previous owner to have registered it to their account and if they don't transfer it to yours, you'll need to e-mail a picture of the unit's serial number to SonicWall. They will then transfer the unit to your MySonicWall account.
Hence if the previous owner had a Global VPN Client License on it, you should get that when it's transfered to your account.