What happens if Merfolk Trickster taps Emmara?
You will still get the token.

Merfolk Trickster's ability does 2 different things, one after the other. Emmara's ability will trigger when the first one happens (tap target creature). 


  603.2. Whenever a game event or game state matches a triggered ability’s trigger event, that ability automatically triggers. The ability doesn’t do anything at this point.


So at that moment, the ability has triggered (but it is not on the stack yet). Then, immediately after, Emmara loses all abilities.

Next time a player gets priority, the triggered ability goes on the stack:


  603.3. Once an ability has triggered, its controller puts it on the stack as an object that’s not a card the next time a player would receive priority.


This ability is not tied to Emmara at all; so it doesn't matter that Emmara doesn't have the ability anymore:


  112.7a Once activated or triggered, an ability exists on the stack independently of its source. Destruction or removal of the source after that time won’t affect the ability.