Who created the Infinity Stones/how did they come into existence?
Doctor Strange has the Time Stone, so does he know about it? Also does he know about all of the Infinity Stones that exist?
In the most recent film (Avengers: Infinity War) Wong provides a nice magical hologram show regarding the origin of the Infinity Stones. It seems fair to say that this isn't news to Strange since he helps with narration and correctly identifies them by colour and name.
Later in the film he describes various things that Thanos will be able to do with various of the Stones, indicating that he also knows their powers.
There's also a mini-origin for the Stones in Guardians of the Galaxy