I'm not familiar with the ES Explorer interface but I'm sure it is similar to Astro. I think the tough part is you can't be sure where exactly the trojan file might be since it could just be linked to Polaris as opposed to being in a Polaris folder.
You'll probably need to look on SDCard0 and search through each folder one at a time. "Download" or "downloads" Folders are good places to start. However, with something like a trojan, if indeed there is one and TrustGo isn't giving a false positive, it may be buried within the Android OS system files which you cannot touch without root access.
The thing that tips me off that you may be OK is twofold. Lookout is not seeing it and TrustGo is not trying to quarantine it. If you can't find it using ES Explorer maybe go to trustgo.com and click on Support>Feedback and see if they'll respond to an inquiry about what you're seeing or email them at
support@trustgo.com.