Substitute for Kirsch in Leckerli (Basel Lackerli) cookies?
I would use any uncolored brandy made from distilled fruit. Himbeergeist, sliwowitz, or what you can lay your hands on. 

Kirsch doesn't taste much like cherries, and I suspect that it functions more as a solvent for some of the aroma in the spices than for adding its own taste. Even though it does contribute a bit, the taste will be subtle, and other slight fruity notes from a different fruit brandy will blend with the heavy spices just as well. 

In a pinch, you could use a colored brandy too, like Chantre. But it will add more of its own flavor, and while it can make a good combination, it will be further from the original than a random obstwasser. 

I would avoid any liqueurs, they will add way too much foreign taste, and also won't have enough alcohol to solve the spices in the same way.