Well if there isn't, you can start the EXE and do Debug|Attach from VS. Or (I think?), you can go to File|Open Solution, open the EXE directly, and let VS create a temporary solution for you that will let you run the EXE as a debuggee by pressing F5.

If you're debugging an EXE without source because you're writing a plugin or addon for it as a DLL, and you want todebug that DLL, you can specify the EXE in question as the EXE to run when you start debugging as part of the properties for the project for the DL in question. Visual Studio will spot when your DLL loads, load the debug info for it, and activate any breakpoints and so on. Works well.

(If your addon runs as a child process, you need the Child Process Debugging tool. Transformative. Get it here: https://marketplace.visualstudio.com/items?itemName=GreggMis...)

When you don't have source code, VS is not the best environment ever - it's oriented very much towards worknig with C/C++/etc., and there's a few options you have to play with to get it to show you disassembly and so on. But it's adequate. (One thing I like about it very much is that the step commands are the same whether you're stepping through source code or whether you're stepping in the disassembly window. I'll put up with quite a lot in exchange for that.)

In Visual Studio 2017 you can open an executable directly and begin debugging it without having either of those things.