Doctors, how much Xanax (alprazolam) can I safely take with oxycodone?

Depends on the dose. The combination of the two drugs can be dangerous. Xanax (alprazolam) is a sedative, and oxycodone can cause respiratory depression, meaning you could get into a situation where you breathing is obstructed and you're too sedated to do anything about it. Talk the doctor prescribing these meds about whether taking any amount of the two together is safe.
Check with your MD. The reason for caution is that this combination of drugs greatly increases the risk of impaired breathing. Breathing rate and depth is controlled by two factors - carbon dioxide and oxygen levels in the blood. Xanax (alprazolam) impairs the body's response to low oxygen levels and oxycodone impairs the respone to carbon dioxide. The two together can produce severe respiratory depression and even death.