How much Deep Pour do I need if wood, corks or rocks fill the pour?

Calculate from the epoxy, not the well. Work out how thick the epoxy will be above the corks, wood or rocks, and use that depth across the full length and width of the pour area. For loose pieces like driftwood, measure the pour without the wood and use the Deep Pour Epoxy Calculator: https://www.bestbartopepoxy.com/pages/deep-pour-epoxy-calculator

The depth above the objects also decides the product. If they sit flush with the top, as with a bar filled with half golf balls, you only need a 1/8" flood coat of UltraClear Bar & Table Top Epoxy. If there's 1/4" or more to fill, use UltraClear Deep Pour Epoxy: 1/2"-thick corks in a 1" well on a 39" x 24" top is a 1/2" pour, which takes a 3 Gallon kit. For something like 5/8", pour 1/2" of Deep Pour, let it cure at least 3 days, sand-scuff it with 220-320 grit, clean with denatured alcohol or acetone, then pour the 1/8" Bar & Table Top flood coat.

Corks, wood and rocks are porous and will release air bubbles into the Deep Pour unless you brush on a seal coat of Bar & Table Top Epoxy first. Corks are very porous: do two or three seal coats 4 to 6 hours apart, then wait 4 to 6 hours before the Deep Pour. Order at least 1 gallon combined of Bar & Table Top Epoxy for the seal coats and flood coat (2 to 3 gallons for a 38" x 72" top).

Full process: https://ultraclear.helpscoutdocs.com/article/859-table-top-epoxy-deep-pour-epoxy-river-table