It wasn't Anakin or The Sith, Anakin was very far away and had no knowledge of the force, also Obiwan would not have gotten a bad feeling if he were sensing Anakin at that time, it couldn't have been The Sith, they were not on Naboo, they were still on Coruscant until the time Maul left for Tatooine, The Jedi came from Coruscant, if the Jedi couldn't sense the Sith while they were on the same planet, why would Obiwan start sensing them clear accross the galaxy ? What Obiwan was sensing was something bad was going to happen in the future, you can tell by the conversation, OBI: "I have a bad feeling about this", QGJ "I don't sense anything", OBI: "it's not about the mission Master, it's something elsewhere, elusive", QGJ: Don't center on your anxieties Obiwan, keep your focus here and now where it belongs", OBI: "But Master Yoda said I should be mindful of THE FUTURE", QGJ, "But, not at the expense of the moment". The reason QGJ didn't sense anything at that time was because Nute Gunray and co, were not afraid yet, they knew the ambassadors had arrived, but didn't know they were Jedi Knights, it wasn't until AFTER TC-14 told them the ambassadors were Jedi that they started to panic and that's when QGJ said "I feel an unusual amount of fear for something so trivial as this trade dispute".