It's an audio bug.
Trakis is shown listening to it as he negotiates with N'grath (scene starts at 31:26 on my DVD copy). The audio conversation they are listening to is Sinclair and Londo bribing the girls at the Dark Star club for clues as to Adira's whereabouts. The last bit of the audio of that scene comes over the link, telling everyone that Adira's friend lives in Brown 6. Trakis immediately uses this to hire goons from N'grath to slow down Londo and pick up Adira before they can, at which point they're forced to come up with Talia as a backup plan.
This does cause a small plot hole, as Londo and Sinclair do arrange Talia's assistance without tipping him off, and he expresses surprise and caution to G'kar when she shows up to "monitor" their negotiations. The bug is never shown to be found; it visibly cloaks itself as soon as it's on Londo, so we can't rely on spying it later. I've seen it mentioned that Londo and Sinclair did something to prevent Trakis from knowing, but there's nothing to support this in the episode, other than Trakis being surprised by Talia. I think it's more likely, given Trakis puts the receiver away as soon as he gets Adira's location, that he simply wasn't listening 24/7. Londo does point out he can harm her if they come at him directly, and the goons harassing them backed off as soon as the job was done, so he may have assumed he had control of the situation as soon as he had Adira.