A good faith question is when you're honestly seeking clarification either because you don't know something or don't know what the other person means.
Sealioning is when you're "just asking questions" in a manipulative manner with no intention of taking the answers seriously under consideration or making a valid point of your own.
It's often used in place of an actual argument when the sea lion knows that their point isn't strong enough to withstand scrutiny.
Here's the origin of the term afaik:
While preparing a ham with a deeply penetrating glaze.