When we are asking about persons swimming "teraz" [now] in a pool - I would rather translate to Present Continous. But "płynąć" can translate also to "sail" and "cruise". if we were talking about a ship or yacht - Simple Present should be OK: "Where do you sail to, now?"
płynąć is only current but it should be noted that "Gdzie teraz płyniecie?" describes an action of eiher swimming or going using boat/ship/ferry/motorbike etc and also well means "water equivalent" of where are you going, not where are you walking? the question is not about the place but destination. I think question should be dokąd płyniecie, it's more accurate.
Pływać is more complicated- as it can mean both now and freqentative, but now it's a movement witout a destination. Gdzie teraz pływacie - np which swimming pool you use this winter can be translated to Where do you swim now?- unless there is an English rule against it
we do, but we are not as strict as Germans. "Dokąd" means "wohin", "gdzie" means both.
On the other hand "płynąć" means to swim right now, with a destination, while "pływać" means to swim usually, or without any destination (like in the pool).
This sentence is more likely to mean "Where are you swimming to".
- General rules of adverb position: https://www.espressoenglish.net/position-of-adverbs-in-english-sentences/ , https://dictionary.cambridge.org/grammar/british-grammar/adjective-and-adverb-phrases/adverb-phrases
- Placing of "now" in a phrase: https://dictionary.cambridge.org/grammar/british-grammar/adverbs-of-time-and-frequency/now