According to a report from MMA Fighting, Jon Jones and Brock Lesnar aren't facing the regular two-year ban for fighters that fail drug tests for the first time. Instead, due to WADA code, they would only be facing a maximum of one year each, and it's possible that they receive as little as a warning. Ariel Helwani explains:
"The reason for the shorter suspension is because the banned substances the pair tested positive for -- Hydroxy-clomiphene, an anti-estrogenic agent, as well the Letrozole metabolite, an aromatase inhibitor, which was only found in Jones' system -- are considered "specified substances" under the World Anti-Doping Agency Code.
Per the WADA Code, "there is a greater likelihood that these (specified) substances could be susceptible to a credible non-doping explanation." When it comes to specified substances, the WADA Code recognizes that it is possible for a prohibited substance to enter an athlete's body inadvertently, "and therefore allow a tribunal more flexibility when making a sanctioning decision."
The article also states the the fighter has the right to go to arbitration if they choose not to accept USADA's decision.
One thing that could cause a big kerfuffle is the Nevada State Athletic Commission. They are the ones that have temporarily suspended both fighters already, and they aren't bound to USADA decisions. They could choose to suspend the fighters for a longer term than given out by USADA, if they see fit.
Jones failed a test for the two substances listed above in the lead-up to his UFC 200 bout with Daniel Cormier, and was pulled from the card just a few days before the event. Lesnar tested positive both before the UFC 200 fight and in his post-fight test for one substance, but the results for the first one didn't come back until after the fight took place. He defeated Mark Hunt by unanimous decision, and made 2.5 million dollars for that night of work.