You can check the current elastic search version installed in Magento 2 with the command line as well as from the admin panel.
If you want to check by Command Line,
php bin/magento config:show catalog/search/engine
The output will be: elasticsearch7
If you have running elastic search version 7, the above output will be displayed.
You can also check it from the Admin Panel.
Go To Admin panel, click on left sidebar Stores -> Configuration -> Catalog -> Catlaog
Now Click on the Catalog Search section, You will be able to see it from the Search Engine Field.
That’s it to check the elastic search version in Magento.