Is saying "君（きみ) RUDE

So, I read an article saying that using " anata " and " kimi " for "you" is a very rude thing to called someone. Is that true? And if so, what do I use instead to say "you" 

To my knowledge, the words themselves aren't rude, the reason why it's rude is cultural. People expect you to call them by their name, rather than "you" and if you use anata or kimi, it's basically telling them you don't remember their name. Hope that helps! (Correct me if I'm wrong) 

 Let's say we're talking to one of my friends (let's say female) how will I say "you" in this sentence in Japanese. 

"What do YOU like about this?" 

Can I use "ANATA" in this sentence. 

こんいちは！

Well, as far I do understand it, you don't use often "you", "I", "he/she" etc in Japanese in conversation ... as normally the context indicates you that your are talking about "you", "he/she" ..., or asking a question to "you". Unless it's not clear, or you want to emphase it,  then you can use the name of the person or the personal pronoun (anata, etc..). 

So in your example, unless it's not clear to the person that you're asking the question to "you", and unless you don't want to emphases that you really want "you" opinion, you drop the "anata". 

Hope this helps, but I'm a beginner too :-)

またね！

~これについて何が好きですか？

I would roughly translate this to, "What about this is likeable?" The "to you" part is implied by asking them in the first place.

If you have a group of people and you only care about one of their opinions, you would use their name or title.

If you wanted it to be more casual, you could even take off the "ですか？" at the end. Japanese is full of leaving things out and knowing it still makes sense in context.