"Siapa suka berenang" should be correct...
That's what I thought. I am reporting it now 7/4/2020
Yes, but "Siapa yang suka berenang" is more formally
Although "Siapa suka berenang" may be 'less formal', it is still not wrong. That's my humble opinion.
My... keyboard.. didn't see that i pressed siaPA and now i got it wrong even though i'm an indonesian yay
"yang" is not required