The answer to 'how to unclog sink' is to use a plunger or drain cleaner. First, try using a plunger to dislodge the clog. Fill the sink about 1/4 full with water, place the plunger over the drain, and plunge up and down rapidly about 10-15 times. If that doesn't work, use a drain cleaner product by pouring it down the sink and letting it sit for the recommended time before flushing with hot water.
If the clog persists, you may need to remove the sink's P-trap or use a drain snake to reach deeper into the pipes. This is where calling a professional plumber may be necessary, as they have the right tools and expertise to safely clear more stubborn clogs.