Riddle said by Edward Nygma to Penguin in Episode 4 of Season 3 of Gotham:
I can't be bought, but I can be stolen with a glance. I'm worthless to one, but priceless to two.
The answer should be "love". What I'm not sure is whether this was a declaration of love between Nygma and the Penguin or anything else...
Some people theorize about a gay relationship hidden there.