According to the strike timetable published, it's still possible to go from Praha to e.g. Amsterdam in one day (so no extra pass day needed).

Of course less comfortable and unsure and I'd avoid it but not impossible. Use bahn.de to see the trains that are running.

E.g. Länderbahn is not on strike so the trains from Praha to München should run if there's no general track closure. You need to have a look on the day.

According to this and according to the rule that Interrail might not be considered a through ticket (you didn't mention which route from where to where you'd go and if you are holding reservations) you won't get accomodation paid in Praha. (Different if you are in Germany and there are no more trains in your direction.)

You do get 12€ for a delay of more than 60min or 24€ for a delay of more than 120min.

I don't see any reservations needed if not going through Germany so no need to pay anything (but of course I don't know where you'd like to go exactly).

You could get an extra pass day via customer service, but strictly speaking that's not necessary because if you get stranded, the railway companies are obliged to get you to your destination anyway.

DB, the German Railways, has asked travellers to avoid travelling during the strike, and that those who do choose to travel, are strongly encouraged to make a seat reservation. 

If you don't have a reservation and the train gets too crowded, travellers without reservation will be asked to leave the train. 

Which day are you coming back ? Where do you have accommodation booked ?

For example it is entirely possible to avoid Germany by crossing Austria and Switzerland. Beautiful Alpine journey too! I can suggest an itinerary :)

If travelling through Germany have a look at DB Navigator app or another reliable resource, they'll tell you which trains run and which don't. Read the fine print and leave early in the day.

From what I know trains aren't really full on strike days (those which run of course!), reservations are still recommended.

You might have a travel insurance in case too.