I realy have no clue as to what the memory task could be, if there even is one
The obvious way to go is the pit stop greeters (Phil did say he wanted to incorporate the greeters more). Two other options did pop up in my head, but it's always incomplete if you go leg by leg.
1) feathers/birds (the 2 birds at 2 pit stops does suggest it)
2) metallic objects on the race (like the St. Ninians artifact in Leg 3 or the candelabra clue holder in Leg 5)
If there is going to be a memory task, maybe they'll go by it like in season 14, where it's just random things you see during the race.