If you log out in space, your ship disappears after 10 seconds of invulnerability. When you log back in, you will be in very nearly the exact same spot, but the instance will regenerate, so if you are at a res the asteroids will appear to have moved.

If you log out in a station but not docked (i.e., in the process of docking or launching) you will be moved to a safe zone about 10km away from the station when you log back in.

If you log out docked in a station but on the surface, your ship vanishes and the pad opens up for another player / NPC. If you log back in and your pad is still available, you will reappear there. If not, you will appear on another pad in the same station.

If you log out docked in a station in the hangar, your ship vanishes and the pad becomes available for another ship. When you log back in, you will be in the hangar, and returning to surface will try to put you on the same pad as before, as long as it is not occupied. If it is, you will be put on a different pad.

If you log out while in super-cruise, you will log back in to normal space; sometimes at the point you entered super-cruise, and sometimes close to the stellar position where you logged out. Seems about 50/50.

I am unsure what happens if you dock at an outpost and log out, and log back in while all pads are occupied; it probably bumps you to an instance where they are not all occupied.