Where do you find the s or d mint mark on a 1916 coin?

You have to know the coin's denomination to locate the mint mark because it can be in different places. Also, Philadelphia did not use a mint mark on most coins until 1980 so many 1916 coins won't have mint marks.

You can check many sites to find mint mark positions listed by year and denomination. A good one is coinfacts.com. It's no longer updated but the information for 1916-date coins obviously won't have changed.