Ear checks take a few seconds and are part of every health check at the clinic (sample note).
The vet looks for redness, wax, grass seeds and anything that might make the ear sore. Dogs with long, floppy ears or that swim a lot are checked a little more closely.
Between visits, watch for head shaking, scratching at one ear or a smell. Book an appointment if you see them; your vet will advise on cleaning.