You can turn on popup messages for pet/client warnings when opening a pet/client card, clicking to make an appointment or at checkin.
Click on File, System Options, Global tab and turn on the options.
You will get these messages depending on what you have turned on.
When making an appointment or checking a pet in, it will show the pet's warning and module warning, Boarding, in this example.
When opening the pet card, it will show the pet's warning and all module warnings.
Here's the owner warning message.
When you check a pet in, it will list the owner and pet warnings together.