Light-spot to eye; reptile to bird; dog to horse; etc. or any fossil that palaeontologists or experts in their field have confirmed as verified evidence of vertical evolution. I will let you choose today's current observeable evidence/evidences...given the theory, the evidences should be observeable in the millions.
Suppose we have Fossil A and Fossil C. The species represented by Fossil C is believed to be descended from the species represented by Fossil A. Suppose you deny this connection, citing a 'gap' in the fossil record between the two species.
Suppose further than scientists discover Fossil B which, based upon observable evidence, is declared an intermediate species between Fossil A and Fossil B.
Do you:
1. Accept this as evidence of evolution.
2. Deny this is evidence of evolution, and assert that there are now two gaps in the fossil record?
But not artiodactyl to cetacean, or synapsid reptile to synapsid mammal, correct? You are looking for one fossil that can be shown to be a transition between what, two orders, two families, genera? Or maybe even higher?