This is the Skant variant of the Service uniform worn in seasons 1 and 2 of Star Trek: The Next Generation.
The charts below depict the rank pins worn on the collar of the uniform to denote rank and note placement of the appropriate designations. The ranks are shown with each division where such rank could be appropriate.
Due to changing information presented in early seasons of TNG and a lack of variety in enlisted ranks on screen, it is difficult to tell for sure what ranks are properly used for enlisted crew. The only rank that is definitively known is that of “Crewman”, which bears an unadorned collar without rank insignia.