Hello Leonid,
with sap.ui.getCore().byId(“Screenname–WidgetID”).mProperties you can see all available properties of the widget.
With sap.ui.getCore().byId(“Screenname–WidgetID”).getProperty(propertyName) you can get the value of a specific property.
This is the generic way, but each property has a specific getter and setter.
For your example of a CheckBox you could do this:
sap.ui.getCore().byId(“Screenname–WidgetID”).getProperty(“selected”) which will return either true or false depending on whether or not the CheckBox is currently selected.
We recommend using the selected-specific getter .getSelected()
Please follow the official OpenUI5 documentation for more information on the available properties and methods: https://openui5.hana.ondemand.com/api/sap.m.CheckBox