Lords can see how many marks their knights have. It's listed on the Politics page under You Knights, or something like that.
The only way the judge can find out if someone is protected is to try and punish them. At that point he will either know that the noble has enough to be immune from punishment or not. He can't tell the exact amount.
No one else can see how many good/bad marks someone has. A knight can't even tell how many he has, unless he keeps track himself.