What is the Hebrew word for lock?

Answer 1

It depends on the context:

lock (as in a lock of hair) = taltal (תלתל)

lock (as in a lock on a door) = man'ool (מנעול )

lock (deadbolt) = bariach (בריח)

lock (as an a device that locks up, or a mental lockup or block) = ma'atzor (מעצור)

lock (a device used in a canal to move ships) = ta shayit (תא שייט)

Answer 2

to knock = nakash (נקש)

knock (noun) = nekisha (נקישה)