How can I get logged in user’s session data from admin-ajax?

wp_get_current_user will get you the WP_User object for the currently logged-in user:

add_action( 'wp_ajax_create_team', 'create_team' );
function create_team() {
    $current_user = wp_get_current_user();
    echo $current_user->ID;
    die;
}