The postcard shows a watercolored artwork by Joanne De Leon entitled Why the Sky is High. Joanne De Leon is an award-winning illustrator who received her B.F.A. from University of Philippines. She currently works as a freelance book illustrator and graphic designer. Her illustrations have appeared in many children's books.
I couldn't find additional information about the painting nor its location (private collection or museum). The artwork depicts one of the Philippines folklore. Full story can be read here.