CVI has some mouse events. The Programmer's Toolbox adds more.
In the callback for the control or panel you want to watch, you can add cases for the following events:
EVENT_LEFT_CLICK
EVENT_LEFT_DOUBLE_CLICK
EVENT_RIGHT_CLICK
EVENT_RIGHT_DOUBLE_CLICK
The following additional mouse events are available after you load the Programmer's Toolbox and call EnableExtendedMouseEvents().
EVENT_MOUSE_MOVE
EVENT_LEFT_MOUSE_UP
EVENT_RIGHT_MOUSE_UP
If you want to check the mouse status in combination with another event, you can set a global in the mouse event, and then check the global later.
The normal CVI programming paradigm is event driven: you don't check the mouse status on demand but you watch for events and save status you want from events.