The term "exch_h" represents vertical thermal diffusivity in the MYJ, YSU, QNSE, MYNN, and BouLac schemes. WRF does not output eddy viscosity. It can be extracted from the MYJ PBL in a similar way to exch_h, but would require some coding similar to exch_h in the MYJ module, in addition to a new array. AKMK is a local array in the MYJ PBL that is proportional to the eddy viscosity. XKMV and XKHV arrays are used by other PBL options (not MYJ).