I don't have a fork lift, but I have Google. Not sure which one you have, but I found this... Trans dipstick/fill is on the top of the differential, between the cowl & mast assy
What model and roughly how old? The older automatic ones had fill and drain plugs, like an old manual trans. I think the later ones had a dipsick type deal beneath the "floorboard". This was on the little ones, like warehouse stuff. Have no clue about the big ones.