Get cursor position with respect to the control - C#

Use Control.PointToClient to convert a point from screen-relative coords to control-relative coords. If you need to go the other way, use PointToScreen.

You can directly use the Location property of the MouseEventArgs argument passed to your event-handler.

private void panel1_MouseMove(object sender, MouseEventArgs e)
{
    Text = e.Location.X + ":" + e.Location.Y;      
} 

The following will give you mouse coordinates relative to your control. For example, this results in (0,0) if mouse is over top left corner of the control:

var coordinates = yourControl.PointToClient(Cursor.Position);