In the Flixbus app for the iPhone you can see the stops, for a bought ticket.
Alternatively, you can search the connection printed on the ticket (
<number> <final_destination>) and you will find the timetables on some website which lists the timetables of multiple companies.
What Flixbus Support said (original answer)
I've just talked to someone from Flixbus support and they don't have this data in a public format.
Only they can see it and one who wants to know the timetable, can ask them on the phone.
Using the route map one can see the direct connections between the cities, so assuming there is a direct connection between
D there will be direct connections between
D, but those will be guessed—as the person from Flixbus said: You can play with that map.