If you are doing UDS communication, then you can read up, and look at the examples I linked to earlier. It is not specifically for NI-XNet but shows how you can perform requests and read responses using UDS. If you want to use an official NI toolkit, look into the Automotive Diagnostic Command Set toolkit by NI. It performs UDS communication, either with NI-CAN hardware, or the newer NI-XNet hardware.
@xiaosanhe1224: if I may add my two cents to the probably still coming answer of GerdW... The multiplexing can be sorted out using a DBC. I personally never worked with CAN under LabVIEW and cannot say that for sure, but I doubt that any VI, no matter if NI-CAN or NI-XNET, has an extra function for multiplexing.
This is incorrect. The XNet database editor allows you to import a DBC, or create one from scratch. From LabVIEW you can reference this database, and read and write muxed signals and the API handles the conversion for you. The Frame Signal conversion code I linked to earlier also handles muxed signals.