Question mark in macOS "Messages".

Welcome to the Apple Support Communities!

I understand that you observe an unexpected behavior when you send an emoji in the Messages app on your Mac as the emoji presents a question mark. I will be glad to offer you some suggestions that might help you.
You mentioned that you've reinstalled macOS High Sierra and the behavior continues to happen in your Mac. However, I am not sure if you've tried using a new account that does not have any of your previous documents and data.
I'd like to ask you to first try to create a new user account in order to test if the issue is relating to the settings:
How to test an issue in another user account on your Mac
Pay close attention to the following section:

If the issue doesn't happen in the other account

If the issue doesn't happen in the new user account, the issue is related to the settings or files in your own account.

If you need help with a specific alert or issue, search the Apple Support website for the text of the alert. If the issue happens in only one app in your account, it might be related to one of that app's settings. Check the app's documentation or support website for help.

You can remove the new user account when you're done testing. Follow the steps for creating a new account, but click the Remove button (–) instead of the Add button (+). Before removing the account, make sure that you don't need any of the files or settings you created or copied in that account.

If the issue happens in the other account

If the issue happens in the other user account:

• Make sure that your software is up to date.
• Try using Safe Mode to resolve the issue.
• Check for other software or hardware issues.

Hope this information is helpful. Let me know if you need additional help.
Regards.

Hi,

In Messages Menu > Preferences > General what Font have you set ?

Also, (and more likely) in the View Menu and Substitutions do you have Text Substitutions allowed for Emojis

9:37 pm Saturday; December 2, 2017

Hi,

My bad.

Edit Menu

7:29 pm Monday; December 4, 2017

hi,

I will wait on that and trying the Safe Boot from the first reply.

8:19 pm Tuesday; December 5, 2017

Hi,

A Restore (Start the computer holding down CMD and R) will keep all your data and that of any other Mac User account untouched.

Rather than doing the the First Reply from the Community Specialist has some other thing your should try like the Safe Boot and NVRAM reset

Then I would open Font Book and use the Restore Standard Fonts from the File menu.

8:54 pm Thursday; December 7, 2017

for the Points and for the Points.

7:28 pm Friday; December 8, 2017