Where do you find doctor Domsky
Solution 1:
After the colony ask you to bring a doctor, when you reach the Blue Sector again, you will find a free hint that where he could be. This give you a very good idea about his exact location. Or you can spend 40 rare iridium particle to locate it on the map.
Spoiler lvl1: Tortuga
Lvl2 spoiler: When you reach the tortuga station, talk about slavery. You will see a third option to ask whereabouts of Dr. Domsky.
Spoiler level 3: After you gain the information, another location will be revealed on map. At that station you'll find him. 3 command points or 10 rare iridium particle will convince him to join your crew.
Spoiler level 4: If your passenger capacity is above " full capacity minus 5(or 6)", your chance to bring him to onboard with 3 command point will be low. But you can always persuade him with 10 rare iridium particle in the end.
P.S: I tried to write like UHS hint system to not spoil the suprises.