Class names of Windows controls can be looked up with different tools, like Spy++, AU3_Spy.
When using AU3_Spy the class name is displayed in the section "Now Under Mouse Cursor" when the mouse is hovering over the respective control:
Note that the class names have number postfixes which must be stripped off. But at the same time, numbers can be part of the class names, for example SysTreeView32, as shown in this example. To find out whether the numbers are part of the class name or not you may need to try all possible variants, but in most cases assuming the "32" is part of the class name is a pretty safe assumption.
Related Information: