One Stack, Two Queues
I don't have an actual answer, but here's some evidence that the problem is open:


It's not mentioned in Ming Li, Luc Longpré and Paul M. B. Vitányi, "The power of the queue", Structures 1986, which considers several other closely related simulations
It's not mentioned in Martin Hühne, "On the power of several queues", Theor. Comp. Sci. 1993, a follow-on paper.
It's not mentioned in Holger Petersen, "Stacks versus Deques", COCOON 2001.
Burton Rosenberg, "Fast nondeterministic recognition of context-free languages using two queues", Inform. Proc. Lett. 1998, gives an O(n log n) two-queue algorithm for recognizing any CFL using two queues. But a nondeterministic pushdown automaton can recognize CFLs in linear time. So if there were a simulation of a stack with two queues faster than O(log n) per operation, Rosenberg and his referees should have known about it.