what are the safety requirements for scraping old drylock?
Your primary concern would be with any lead-containing coating beneath the Drylok. Your secondary consideration should be for silica.
According to the CDC, an N95 is NOT adequate for lead dust, you need a P-100 or equivalent rating on your respirator.
For airborne silica dust, an N95 is acceptable.
So if you are relatively confidant that there isn't an old lead-containing coating beneath the Drylok, the N95 would be sufficient.