Coding
There's nothing to step you writing the code itself; IDEs are just fancy text editors with other tools built in (in the case of Visual Studio, a full code translation toolchain).
You'll probably find that things like code completion won't work, as JUCE will #ifdef
parts of the codebase out depending on what project type you're launching, but last I checked (when I worked there) there was no Visual Studio iOS project exporter available, so you'll have to just use a Windows compatible one and program through that.
Building
In order to build an iOS app, you need a Mac. If you take a look at the documentation, it states:
For iOS projects, connect to a networked Mac and start the Mac emulator from Visual Studio.
No cross-platform library that I know can circumvent this restriction; I believe it's due to a legal requirement enforced by Apple.
With that said, if you don't own a Mac you might be able to "rent" one using a service like Mac In Cloud. I'm not a lawyer, some please make sure you check the legality of using such a cloud service for building iOS apps before doing so.
Debugging
Since you need to be able to compile in order to debug a specific build of the application, the section on building applies. Of course, there's nothing stopping you from debugging it without a build by reading the source code carefully, but I'm guessing that's not what you're asking about.