Ok, so without looking (and forgive me my vocabulary is really lousy from disuse)

My strategy for compound words is usually to try to break up the word, starting at the end, since mostly they are nouns with a bunch of adjectives stuck in front.

Donaudampfschiffahrtsgesellschaftskapitän

So kapitän is easy since it’s a near cognate for captain.

Gesellschaft looks like a word i used to know, but I can’t remember it.

Schiffahrt - i don’t know this one, but it looks like schiff (ship) plus fahren (to go) - shipping?

Ampf - no clue

Donaud - I feel like this must be modifying ampf, because it doesn’t look like a word on its own, but since I don’t know ampf I am stumped.

So my guess is someone in charge of something to do with shipping.