When looking at the application designer, we can see application ID in the link:
It is the same appid that will be added to the url when you open your application in Dynamics:
However, try adding that application(and the corresponding sitemap) to a solution, then export the solution, and have a look at the customizations.xml:
You’ll see the name of your application, but you won’t see the ID. You should probably see where this is going at this point, but let’s do a test.
Delete your application sitemap, and, then, delete the application from your Dynamics instance. Publish all customizations. Make sure the application is not there anymore. Re-import the solution exported above back to your Dynamics instance.
Your application will be back, but it will have a completely different ID:
Why would it even matter? Mostly, because there can be multiple applications in the Dynamics instance, and you may want to start adding application ID-s to the links you are sending by emails or using in the reports. And, if you follow some kind of application lifecycle methodology, you will likely have a dev environment where your application ID will be different from the same application ID in production.
Just don’t use the ID directly or you’ll have to re-configure the workflows/scripts/etc every time you deploy them in production as part of your solutions.