Comment 1 for bug 1615575

There are some emoji in the Small and Phone layouts.
Small: press "12?", then "☺" on the SHIFT key.
Phone: press "12!@" then "1/3" twice
It's a limited selection in both cases, though.

The other layouts don't have any, although there's an older branch were they do:
https://code.launchpad.net/~onboard/onboard/layouts-experiments
IIRC, the problems back then were a) all those new keys dragging down performance, and b) disagreements on if/how to place the emoji button on the main layer.

I believe we would be better off with a scrolling popup list. That way we could offer all the emoji+descriptions without having to add a myriad of keys to each layout. I'll discuss this with Francesco when he's back. He's worked on the emoji support before.