Which one is grammatically correct or better to use?
About before pronoun:
I haven’t listened to the album about which you were talking.
About after verb:
I haven’t listened to the album which you were talking about.
They're both technically correct. I would personally prefer the second one, though, as it sounds more natural.
Students of English used to be taught that it was bad grammar to end a sentence with a preposition (like "about"). Following this rule produces sentences like your first example ("about which you were talking").
However, this "rule" is derived from Latin grammar, and English isn't Latin. This "rule" has been falling out of favor since the beginning of the 20th century, because it can produce sentences that don't sound natural. You can end a sentence with a preposition, but you don't have to.
There are many, many articles about this; here's one from Mirriam-Webster.
Ah, well, this gets into the "ending a sentence with a preposition" debate. Some people think it's fine, others don't like it.
Personally, I'm in the middle and avoid doing it if possible -- unless the alternative is even more awkward. So, in this case I would say it's fine to have "about" at the end:
I haven't listened to that album you told me about.
Or use a different verb:
I haven't listened to that album you mentioned.