serious answers only please without me calling a plumber
Use a shop vac that is approved for water, or disassemble the trap.
If it's where you can see it, that is not all the way down to the trap try this. Chew up a wad of gum and stick it to the bottom of a pencil or chopstick then push it down there to stick it to the cap and pull it out.
The pop-up drain plug in most bathroom sinks can be removed by giving it a quarter turn and lifting it out of the sink. Then loosen the 2 nuts under the sink on each end of the trap and remove it. There is a little water in the trap to prevent sewage gases from coming back into the home so be careful not to spill it after it is removed. Then simply dump it into a bowl or bucket and reassemble in reverse order that it was taken apart after cleaning out any "gunk" you might see inside the drain.
