Hi,
It's possible. First, you need to open your PHPMyAdmin and run a MySQL query to change the charset of the hikashop_config table.
For example:
ALTER TABLE #__hikashop_config CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_bin
where #__ is to be replaced by the prefix of your tables.
Once done, you should be able to add emojis in the subject of your emails.
Note however that not all emojis might not appear the same and might not be supported by the different email clients. So make sure you carefully test the results on different email clients.
You can read more about all that there:
stackoverflow.com/questions/39463134/how...er-in-mysql-database
docs.smartrmail.com/en/articles/1932535-...ing-emojis-in-emails