You can create default tooltips for feature classes using the Model Explorer. Asset or subset selection-based tooltips created from the Properties pallette override default feature class tooltips created from the Model Explorer.
Click Manage
Model
in the Toolbar to display the Model Explorer.
In the Model Explorer, right-click the row for the feature class whose tooltip you are creating.
For example, right-click Roads.
Click Select All to apply the Tooltip to all objects in the feature class.
Right-click the feature class row again and Click Set Default Tooltip to open the Edit Tooltip window.

Enter Tooltip content.
Click OK.
Click Update in Properties Palette to replace existing Tooltip content, if any.