This article outlines how to best go about getting support. It is recommended to make sure you try these measures in this order, moving on to the next measure only when the previous has been exhausted.
1. Check the docs
2. Have a chat
#nixos IRC channel on the Freenode network is very active, and is one of your best shots at getting live support; if you don't have an IRC client you can use Freenode's own webchat or alternatives like KiwiIRC.
3. Post your issue
If your issue is technical and possibly a bug, you can report the issue on the Nixpkgs GitHub repository. For other questions, you could try the stack overflow, the nix-devel mailinglist or the NixOS Reddit channel.
4. Hire a pro
If all else fails, you can hire a professional Nix consultant; see the list of Nix consultants