Alpha and Beta Quadrant star chart which depicts the Marnak IV's location
Manark IV was a planet in the Manark star system, which was outside Federation space. (TNG: "Conspiracy")
It was the homeworld of the sand bat. (TOS: "The Empath")
Manark IV (misspelled as "Marnak IV") was seen as a small note on a very large star chart graphic created for "Conspiracy". It was the image behind the chair in the room where Dexter Remmick was killed. It appears to be located outside of the outlined blocks, which may indicate that it was outside of Federation territory at the time.