For Interrail ferry discounts, check:

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

Although I doubt if there’s a discount to Egypt. To find ferries to Egypt, try Google.

I really doubt very much if there is any ferry at all. Perhaps, perhaps-but thats also quite unlikely, there MAY be a ferry-certainly not daily, from EG to Greece, then go onward. EG-somewhere in Turkey seems more likely to me, and from there its more easy overland+sea onward.

Flor these things google is your best friend-as always, or use a general touristy forum, like the old lonelyplanet/thorntree or tripadvisor.

There MAY perhaps, perhaps, also be a cruiseline that will also take passengers on just part of its trip-likely ´around the eastern mediteranean´, if possible, there will be just a very few trips/year and high prices..

Follow up-out of curiosity I did the googling. There are dozens of sites that offer to book any ferry in the world-the most promising even mention a line from EG to IT-but they accept booking with CAR only.

But nothing showed up. 

There are also (Alexander, you ask more often here-so learn to use these other sites for quick result) sites that promise to offer any link-they only show flites. F.e rome2rio.

Oh-then I remembered that trustful site for aficionados of trains: seat61, by Mark Smith- it describes all the possible overland+sea routings from the UK to other countries. So simply hook on somewhere in the middle if youre not british. It has the full story-that 3 such ferries have started and gone down in a year-the last one already 10 years ago. Also no link to een Turkey. So by now its simply impossible-due to actual political situation in countries you would need to cross overland LYbia or Syria.