Is it possible to read a result if wp_update_user or update_user_meta fails?

Not really. Deep down such functions are essentially writes to database. So either database write fails (which doesn’t produce meaningful message to return) or data is somehow wrong and function just returns false to escape.

Your best bet is probably to control data user inputs, not result of WP trying to process that data.

PS worth mentioning that for debug WP_DEBUG and wpdb error echoing rock, but it’s not exactly what you are asking for.