If I attach a Grass Energy to Skiploom with the "Solar Evolution" Ability but there are already 4 Jumpluff either in play or in the discard pile, can I still search my deck for that Pokemon and fail?

You cannot use Solar Evolution to search your deck since it is public knowledge that you won't find any Jumpluff if all four copies of the card are in known areas.

Relevant cards

SWSH7_3