The one sporting Polish colors is a Yak?

And is the other a Lavochkin?

It appears to be, yes. A LaGG and a Yak.

Very nice!

:D Can you tell which is which?

The Yak, if I recall correctly, was a basic fighter airframe with a jet engine under it. The jet on the left has the right silhouette for Yakovlev's early effort.

The LaGG was also a transitional form, with the engine completely buried within the fuselage.

Do I get a cookie?

NO. I am not aware of the development of either aircraft, but I can tell them apart by familiarity and experience. The Yakolev has rounded wing surfaces, the Lavochkin's being more square. The Lavochkin is also larger. The Yakolev has a two piece bubble canopy rather than a divided front one. Also noticeable are the MG's, the Yak's protruding out. And the easiest way to designate the two... the Yak's intake has no vertical support.
...but you get a cookie anyway for naming the producers of these two similar craft! ^^