fruit flies?

Here is a link that might be useful: fruit flies

Drain flies. Put some strips of masking tape or tape across the drain of your sink, leaving a bit of opening. You'll know then if they are actually coming from the drain if you find several stuck to the underside/sticky side...

Here is a link that might be useful: Drain flies which are different from fungus gnats or fruit flies

Those look like flying ants to me. Ants fly (swarm) to find a place to set up a new nest.

Here is a link that might be useful: Flying ants

They look sort of like termites, which grow wings and recolonize once per year. Usually the hottest time of the year is when they swarm.

They are flying ants. Termites don't have a "waist", which those clearly have.

How do you get rid of flying ants when you cannot find where they are coming from? They do not follow a trail like regular ants. They just fly-in and land by a light. No evidence of them elsewhere. Can you use a bait to eliminate the nest? Terro does not work.

OMG!
Looks like the flying ants. could be dangerous enough. I suggest you to call up the pest control company, till then wash you sink with good cleaner.

They could be coming up from some other drain and going over to this one because of the moisture. Presumably you use this sink regularly so the trap is full of water. Make sure all your other drains have water in them. Sometimes an unused shower stall or floor drain dries up so bugs can come up from the sewer. It's a good idea to put some water down unused drains every few months.