For "cookie on nose" you should first work on getting him to sit-stay while you do different things (walk around him, pick up front feet, look in mouth/eyes/ears) then work on holding his muzzle WITHOUT trying the trick. Pet him, talk to him, do different things to make him comfortable while you hold his head/muzzle. Then start working on the trick.

Not so sure about what to do with the "sneeze". After making him comfortable with you holding his muzzle still, hold his mouth closed when trying to do this. If he doesn't especially like you holding his head still, I'm not so sure on how he is going to react to you hold his head AND blowing in his face. Everytime I blow in Autumn's face/ nose, she gives me a kiss.