Determine the name and priority of the currently called action/filter callback in WordPress.

wp-action-name-and-prio.php

<?php

/**
 * Output the current action name and priority.
 */
function pst_action_and_priority() {
	global $wp_filter, $wp_current_filter;

	// Find the currently running WP action/filter name.
	$action = end( $wp_current_filter );
    
	// Get the corresponding WP_Hook object of that filter.
	$filter = $wp_filter[ $action ];
  
	// Determine the priority of the current filter callback.
	$prio = $filter->current_priority();
    
	echo "Action $action [Prio $prio]\n";
}

add_action( 'login_init', 'pst_action_and_priority' );
add_action( 'login_form', 'pst_action_and_priority' );
add_action( 'login_form', 'pst_action_and_priority', 1 );
add_action( 'login_form', 'pst_action_and_priority', 100 );

/*
Output:

Action login_init [Prio 10]
Action login_form [Prio 1]
Action login_form [Prio 10]
Action login_form [Prio 100]
*/