You right-click on the asset with missing dependencies (in Content Manager), and click "View Dependencies". There you will see which dependencies are missing. If you are lucky, these will be on the DLS. If that is the case, click "view in main window", and simply download the ones that are not already downloaded.
If, however, the dependencies are marked as "Unknown", you have to do a google search for the dependencies, and hopefully you will find them. Right click the unknown dependencie, click "Copy", and Ctrl-V it into the search field in Google. You might want to remove the "Unknown Location"-part, so that you are left with only the kuid itself in the search.
Getting hold of unknown dependencies can be quite alot of work. However, it is satisfying when you are done

. If you are absolutely unable to track down dependencies, post them here, and someone might know where to find it.
Good luck.