"Who knows how to swim properly?"

Translation: Pwy sy'n gwybod sut i nofio yn iawn?

[savandwich]

I thought if the preceding verb ending with a vowel, you had to add "'n" instead of "yn"? so it would be "nofio'n iawn" ?

[MrGWallCymraeg]

That is correct :) In spoken Welsh, you can't really hear the difference between the contraction and not.

[savandwich]

Oh right I get it :) thank you!