How many tubes required to bond 0.2" x 4' x 8' plywood underlayment to wood substrate?

65 tubes should do it ! good luck .

To bond a piece of .2" X 4' X 8' veneer to a plywood substrate I would not recommend using Liquid Nails from a tube. I would use liquid contact cement. You can use a squeegee to thinly level the contact cement on both surfaces and follow directions when to overlaying the veneer. Follow up with a laminate roller to insure a completely flat appearance surface. If you use the liquid nails you will not be able to get it thin enough to have complete uniform adhesion. The verneer will not lay completely flat and will result in a poorly executed job.