This is a very good question. You would think that packages and software would tend to have clear names. But they don't always.
The simplest is a net Search on the package. You can usually find the name this way pretty quickly.
You can also run in terminal:
apt list --installed
This will list All Installed software on your system in alphabetical order. You can scroll to your package name to get an exact name. I like to save a copy of this list in the Documents folder for reference, especially if I do a wipe and reload, so I know what to install.
Similarly, you can use apt-cache:
apt-cache pkgnames | less
What makes this useful is that if you only are guessing at a package name or are not sure, you can use the apt-cache to search in a more general way by using:
apt-cache pkgnames (Search Term) | less
So let's say that you know the application is a gnome application, but you are not sure what it is. In this example, you would put in
apt-cache pkgnames gnome | less
And this will list all gnome packages.