When I switch a Prize card and a card from my Deck with Rotom's "Mischievous Trick" Poke-POWER, can I look at either card?
No, you cannot. Keep both cards face-down when you switch them.
Source: Undaunted FAQ (2010-09-09), PUI Rules Team (2010-09-09)

Relevant cards

Note: All applicable cards may not be listed below.
HGSS3_20