Considering Thor didn’t find out about them and their name until Age of Ultron?
shareThanos told him, probably. I mean, he was sent there with an army & also to secure the Teserract(Space Stone)
shareI have serious doubts that the writers of Loki even watched the previous Loki appearances before writing it.
shareThor's vision wasn't that the infinity stones existed, but rather that someone out there was looking to gather them all and use them together in a fist-shaped object, and that Vision would be the key to long-term success.
Asgardians already knew about the infinity stones in general. Lots if MCU characters did.
The Asgardians knew the tesseract held one & that the aether was another, which is why they gave the aether to the Collector in "Dark World." They used the term "infinity stones" explicitly.
And of course the Collector knew with the Aether in his collection, he had "five more to go."
The Asgardians had to know about the power stone on Xandar, because Thor mentioned it specifically and casually.
Back on earth, Wong knew all about them before Stephen Strange ever came along.
It’s not clear whether Loki knew about the mind stone in the scepter.