To make a positive identification with the help of a partial fingerprint, the points of similarity should be at least -
For this different textbooks have given a different number:-

Parikh  → 16 characteristics
Reddy  →10 - 12 finer characteristics
Seth and Simpson → 16 - 20 characteristics

16 is given in more number of textbooks, so the answer is 16.
10
12
16
20