2 and 3: "Who" is a singular pronoun. It takes a singular verb.
In the first, "everyone" is considered singular, so it takes "compliments".
Student or Learner
1. AFTER THE DINNER EVERYONE COMPLIMENTS THE FOOD.
-why not "everyone compliment"?
-Everyone are they (everyone)
2. WHO HAS FORGOTTEN TO DO THEIR HOMEWORK?
why not "have forgotten"? They have forgotten, i have forgotten...
3. WHO NEVER LISTENS TO MUSIC? ; WHO SAIS THAT HE IS NO GOOD?
Why not"who say that"?
We don't compliment food. We compliment the chef/cook/host/hostess on the food.