There don't seem to be ferries to Turkey with an Interrail discount:

https://www.interrail.eu/en/plan-your-trip/trains-europe/ferries

You could try Google...

There is no discount with interrail.

In summer 2021 ferries between Greece and Turkey were not running due to Corona and no one knows if they will run in summer 2022 or not…usually there are many ferry options e.g. from Bodrum, Cesme, … to different Greek islands.

As for now all suspended-reasons logical if you follow news.

There were also a very few long-dist ferries, even from Italy-also suspended.

Note that IR is Turkey is generally a very bad buy: local fares will be much cheaper as even most traveldays.

PS-generally best site for best uptodate info re these links is seat61.com, it overviews all routes most by train from the UK-just use it from a convenient point somewhere oon the continent