There’s probably a better way, but the way that works for me is apt show <package> and then copying everything from the Recommended section into an apt install command

Edit: people in forums are suggesting the simpler apt install --reinstall --install-recommends <pkg>.

I find this preferable because it means the recommended packages get marked as auto, which means an uninstall will automatically remove them.

On the other hand, it forces a redownload and install of <package> which might be unwanted. If you want the best of both worlds, you’re going to have to manually install the recommended packages, then also manually apt-mark auto <list of packages>—although that might make them immediately susceptible to an autoremove, so this might require some tweaking; I’ll work it out when I have time.

If you want to always install recommended packages, add APT::Install-Recommends "1"; to your apt.conf (which just includes the --install-recommends option by default, behind the scenes)