There is no grid method that does this, so you will have to write your own. Here is a rough try at it. You will probably have to tweak it. It starts at the top and moves down until it finds the right row. You coulf try using a bunary search instead of this linear search if performance is a problem for you.
private int GetRowAtNegY(int y)
{
if(y >= 0 )
return -1;
int y0 = this.gridControl1.ViewLayout.RowColToPoint(1,1, GridCellSizeKind.ActualSize).Y;
if(y0 >= 0)
return -1;
int i = 1;
while(i < this.gridControl1.RowCount && y > y0 + this.gridControl1.RowHeights[i])
{
y0 += this.gridControl1.RowHeights[i];
i++;
}
return i;
}