Who plays with me in the league and what players do they own?

Manager Mode
If you tap on "LIGA" in the menu and then on "Table", you will see all managers who play in a league with you.

Tap on the manager to open his profile. Then tap on "Team value" and on "View team" to see his squad.

Challenge Mode
Here you play with every manager who has joined the Challenge. Tap on the manager to see the list of his rostered players.