Jace, Architect of Thought

For each library, the search is complete only when you explicitly say it is. For example, you can look through one player's library, set that library down, look at another player's library, choose a nonland card in the first library, then choose a nonland card in the second library. Don't reveal any cards from those libraries to any other player until you exile them.

When resolving Jace's third ability, you search each player's library (including yours) and exile the nonland cards before casting any of them.

Jace's first ability creates a delayed triggered ability that triggers whenever a creature an opponent controls attacks. It doesn't matter which player or planeswalker that creature is attacking.