one way shear calculation

There should be a detail report for the the design strip under consideration. In that detail report, you should see the location of the governing Vu.

The program uses the plate corner forces to come up internal forces at each of the design sections / cuts in the strip. You should be able to get essentially this same number by plotting these corner forces and adding them up over the width of the design strip.... though this can get complicated if your mesh doesn't line up nicely with your design strip.

The Phi*Vn should be really straight forward. I don't have the code open in front of me. But, isn't it always just Phi*(b*d)*2*sqrt(f'c)? Where b would be the width of the design strip and d would be the depth to flexural rebar.