You can confirm your Algolia extension version by opening your site in a browser and typing algoliaConfig in your browser's Dev Tools console. You can open your console using Option + ⌘ + J (on macOS) or Shift + Ctrl + J (on Windows/Linux).
For example, we can see that version 3.9.0 is running on the store shown below:
It is also possible to check the version in your Composer file, but the console method has the added benefit of verifying the version on your actual front-end.