It's 1917, which means Germany will have to put everything into a last-ditch effort. On the plus side, they are winning against Russia (the war as such is practically over on the Eastern front), but the German economy is on its last legs, strangled by blockade and overtaxed by war production demands. Brest-Litovsk changes almost nothing at sea, so breaking the blockade is out (the German naval assets in the Baltic are derisory, and even if they had actually been handed the Russian fleet, their chances at beating the Home Fleet are next to nil at that stage). Knocking secondary allies out would not be decisive, so while an all-out attack on Italy would be possible, it wouldn't accomplish anything. My guess is, pretty much as OTL - a massive offensive in the West to knock France out of the war.
Realistically, their best bet is to force negotiations on a status-quo-ante basis. In effect, that would be a French defeat, because the country has been bled white and is practically owned by US creditors. Germany would also be in a similar state, but could use its conquests in Eastern Europe to try and stabilise itself internally. Of course, realism was not the strong suit of Germany's leadership, so it's more likely they'll try for a decisive knockout blow and fail. Who collapses first then is iffy - neither side had much left to stand on.