Here's how I increased the font size in the Zorin menu and task bar items (including date/time) as it was all too small for me:
The font in the Zorin menu and taskbar is controlled in gnome-shell theme. I edited the gnome-shell.css file in the Zorin theme tolder.
First, I copied my theme folder from /usr/share/themes to ~/.local/share/themes before editing, so I leave the original unchanged. If you copy without using sudo you will own these files, so editing does not require admin. privileges.
The change you make here has higher priority and will be used by the system instead of the default location.
Location of file in theme folder (using ZorinGrey-Light as an example):
ZorinGrey-Light/gnome-shell/gnome-shell.css
In the gnome-shell.css file, look for this section:
/* Global Values */
stage { font-size: 10pt; color: #29292a; }
and adjust the font here. I changed it to 12pt. Save it and done.