Generally by context, since Polish doesn't really have that distinction, but for verbs that have iterative form of imperfect aspect you can use it to carry similar/same meaning:
"Who drinks coffee? (on a regular basis)" = Kto pija kawę?
"Who is drinking coffee? (right now)" = Kto pije kawę?
Although that use is considered dated/archaic in certain dialects now.
Yes, "kto" always uses 3rd-person-singular masculine forms for verbs, adjectives and so on, so:
- Kto jest zielony? (Who is green?)
- Kto gra na pianinie? (Who is playing the piano?)
- Kto chce zostać strażakiem? (Who wants to be a firefighter?[literally: Who wants to become a firefighter] )
And so on and so forth - in that respect Polish is just like English, where "who" uses the 3rd person singular conjugation too.
Thanks my friend... Actually Who does drink coffee? is not incorrect but carries a different sense... it is like someone is doubfut if anyone drinks coffee so it seems like the emphasis is on the word "Does". Thanks a lot and I had realized that in the beginning but still I was wondering if sense is not being understood by me.
If you have ever watched the French movie "RRRrrrr!!!", the Polish-dubbing version names one of the characters (a girl from another prehistoric tribe) exactly "Kto", meaning "Who". And absolutely no one in the tribe of main characters can pronounce it correctly, which is surprisingly hilarious :D