It seems like the current Komento version doesn't support the emoji and this is why it shows a question mark in the comment.

Can you try to execute the following SQL queries in your database then try to add a new comment and contain emoji and see how it goes?

ALTER TABLE `jos_komento_comments` CHANGE `comment` `comment` TEXT CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL;



ALTER TABLE `jos_komento_comments` CHANGE `preview` `preview` LONGTEXT CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL;

Remember do the full backup first and replace jos_ with your current table prefix before execute it.

For the existing question mark, you have to manually delete it from the backend, edit those existing comments.

Yes its helped. Emoji from a mobile phone are now works.

Will test for a while

Sure, keep us updated then.