Have you tried "preferences => user interface => theme" to change the general font there?
If there is nothing, you will have to edit the X11 preference files for NX directly.
Production: NX10.0.3, VERICUT 8.0, FBM, MRL 3.1.4 | TcUA 10.1 MP7 Patch 0 (10.1.7.0) | TcVis 10.1
Development: VB.NET, Tcl/Tk Testing: NX11.0 EAP, NX12.0 EAP
How to Get the Most from Your Signature in the Community