Can anyone tell me how to get a working doppler effect? All I found in this matter is a “Doppler”-node for sound cues, but I don’t know how it works and if that’s all that’s needed 
I want to use it with fast-moving projectiles, which are not physics-simulated but move kinematically.
Sound seems very limited overall in UE4 by the way. I used to work with openAL before, which is rather basic and easy to use as far as I know, but even that has more to offer than UE4. For example by setting some global/listener variables you could easily manipulate the playback speed of all audio sources to match the time scaling (slow motion etc.). I don’t see a way to do this in UE4.
After playing around with the Doppler node, I can say that once you add it in, all the Doppler physics are applied to your character automatically. And whenever you call that specific sound cue with the Doppler effect, it will apply itself to your player. The falloff radius and overall radius of the called sound cue will also effect the Doppler distortion. Ask me anything if you need any more help. 
Thanks for answering, working on other stuff atm, but I will try that later.
And actually, there is something i’d like to know as well. Like I wrote in the second post: is it possible to adjust the pitch of all active sound sources to a global time-scale, so that you can have a slow-motion effect?
You can use Set Global Pitch Modulation to set the global pitch. It seems like it’s some sort of mixture of Pitch modulation over Time?
And you can use Set Global Time Dilation to slow down all physics. But since the Doppler effect is also physics based, it will probably get confused.
So you might have to apply the Doppler effect to a sound wave before you import it into your project. For something like bullets you could set a hitbox around your character that activates the sound-cues so you’ll always get that pitch perfect Doppler effect.