Can you show a picture of the painting, otherwise I cannot tell you an exact vanishing point for it.
A vanishing point is where all lines and planes in a picture meet and end.
For example, if you had this picture of train tracks, the vanishing point would be where you can no longer see the train tracks as they fade into the background of the mountains where I have marked.
It is also possible for a picture to have more than one vanishing point.
