Can I determine the level of service (LOS) of an intersection in PTV Vissim?

You can evaluate the LOS for intersections using node evaluation.
The LOS in PTV Vissim is comparable to the LOS defined in the American Highway Capacity Manual (HCM) of 2010.
You will find an example in the training directory: Help > Examples > Open Training Directory > Evaluation > LOS With UD Thresholds.inpx.