Get Taxonomy name from “registered_taxonomy” hook

by

$args is an array, not an object:

function test( $taxonomy, $object_type, $args ) {
    echo $args['name'];
}
add_action( 'registered_taxonomy', 'test', 10, 3 );

EDIT

Using the create_term action:

function my_create( $term_id, $tt_id, $taxonomy ){
    $term = get_term( $term_id, $taxonomy );
    echo $term->name;
}
add_action( 'create_term', 'my_create', 10, 3 );