List dependencies of package that I don't already have installed?
In layman's terms :)
You can find dependencies, recommends and suggests for a package like so:
apt-cache depends package-name
You can limit it to dependencies only like so:
apt-cache depends package-name | awk '/Depends:/ {print $2}'
You can check installation status of these dependencies like so:
apt-cache depends package-name | awk '/Depends:/ {print $2}' | xargs apt list
You can print only uninstalled dependencies for a package like so:
apt-cache depends package-name | awk '/Depends:/ {print $2}' | xargs apt list | awk '!/installed/ {print}'