Ah, the wonderful world of cueing ;)
There is no automatic way to achieve this.
If you are working to video, you can use time sheets & specific scene cues.
If you are doing audio only, you need to decide which is going to be a faster working method.
Pre-map everything & use cue sheets held by each actor, so they know at what time-stamp they need to speak their next cue. Use Cubase's large SMPTE display so they can read the cue times from a distance. This may take a couple of hours of rehearsal, depending on the voiceover actors' skills & ability to stretch or shrink time to hit cues.
I've seen voice actors who first take can hit 28.5 s for an advert voiceover, every time.
Radio DJs tend to be very good at this too; stop speaking right at the vocal - 10 times an hour, 5 days a week.
Get one actor to read his own lines, then read the other lines silently to himself. The second actor then attempts to hit the gaps just right.
This can lead to hesitation if the second actor runs long & hits the first actor's next cue. You can always make a cut & drag the next segment later to compensate.
You could make all these cuts before the second actor comes in & make sure all gaps are too long. you then close them all up later.
Get each actor to read their cues one at a time, recording each to a new track, right from the head of the piece. You then manually place each individual cue along a master track pair later.
This is the easiest, though still a bit of a faff.
It may also be less flowing than the previous method.
