A person who has "attained" is someone who knows much. He/She is a master or expert, obviously.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
If you won't put all your eggs in one basket, you won't be a real master.
Viet is a master of the camera.
My dad is famous for being a world-level master in the realm of pizza delivery.