Whenever I suspend my Ubuntu, and then rewake it, Dropbox does not sync, so I don't see files that I edited on other computers. How can I make it sync?
Did you tried to right-click on the Dropbox icon and check if your Syncing is enabled? You also can find more in the preferences of Dropbox.
One workaround would be to Pause syncing, then Resume it using Dropbox icon's context menu. This will lead to re-indexing the whole Dropbox directory though, so you'll have to wait for it to finish before it starts actual synchronization.