What is the recommended screening frequency ?

That highly depends on the individual and their risk profile. But the best approach in general is to be aware of the signs that are up on these posters you see in every good dermatologist's office. Then you can spot abnormalities immediately and get them checked out professionally. Half of all melanomas are not found by screenings and are self-detected instead.

https://www.health.harvard.edu/cancer/screening-advice-thats...

Perhaps by "An annual checkup is not enough", they do not mean you need screenings multiple times a year. Rather, one needs to regularly examine their own skin in addition to yearly checks by a professional.

An aside for my fellow wookies: moles can form under hair!