You will have to read your LabView documentation - that will tell you what format it requires.

The 8051 knows nothing about LabView; it just "knows" about sending bytes out of the serial port; it is up to you the programmer to find out what LabView wants, and implement it!

Is this an excercise in learning to program an 8051, or are you just trying to take some measurements? If the latter, I think you might be better off obtaining a ready-made data acquisition card/module which comes complete with LabView support?