Whays the difference between 입다, 매다 and 끼다?
이는? Is this a typo?
Adding 이 after person's name is to address him/her as 3rd person (beware it's only for persons you're close with).
For 2nd person you add 아 (after consonant) or 야 (after vocal) after their name.
is it wrong to translate this sentences as "Seoyeon wears beautiful rings everyday"?
You can if the context has been established that Seoyeon has a lot of rings that she wears. Typically, you would stress the plurality of "rings" with the plural marker 들.
No, it is correct and accepted.
Does 를 imply that the ring is known to the listener?
I hate that I 'mispelled' her name and you marked me wrong. FFS.