wpdb get_var is not returning any result (verified mysql query returns only one value)

I guess meta_key is not a number, so you shouldn’t use %d in yous SQL query.

$wpdb->prepare( "SELECT meta_value FROM %s WHERE user_id = %d AND meta_key = %s",$userMeta,$user_id,$practiceKey );  // meta_key = %s not %d

PS. You don’t have to escape table name in this way. You can use

$wpdb->prepare( "SELECT meta_value FROM {$wpdb->usermeta} WHERE user_id = %d AND meta_key = %s", $user_id, $practiceKey );