tooltipAt

fun tooltipAt(
    node: LayoutNode, 
    mouseX: Int, 
    mouseY: Int
): List<Component>?

The tooltip of the deepest node under (mouseX, mouseY) that declares one, or null.

Deepest wins, and children are searched last-first: a node drawn over its siblings is the one the cursor is actually on, and the draw order is what says which that is. A parent's own tooltip is therefore a fallback for the area of it no child covers.