how to simulate mouse hover in robot framework on a desktop application
It depends on the automation library that you are using to interact with the Desktop application. 
The normal approach is the following: 

Find the element that you want to hover on (By ID or some other unique locator)
Get the attribute position of the element (X,Y)
Move your mouse to that position. 

In this way you don´t "hardcode" the x,y position what will make your test case flaky.
Can anyone please let me know how to simulate mouse hover event using robot framework on a desktop application. I.e if I mouse hover on a specific item or an object, the sub menus are listed and i need to select one of the submenu item.