Does anyone know how to the henna design on the cupcakes or cakes or when I can find a tutorial for that.
Any help will be great.
You can either paint or pipe the design.
In fact, traditional mehndi is applied with a cone - very similar to piping.
So, just about any YouTube video can be of help.
If you don't want to pipe, hand paint with either airbrush colors, thinned gel colors or colored cocoa butter.
Mehndi are traditionally repeating patterns, so creating a seamless pattern is easy because there is no right or wrong way.
For cupcakes, consider hand painting on pre-cut circle edible printer sheets. Paint 'n apply....
A good design source is Dover Publishing's Mehndi Design. There is a choice of either a basic book or a book with companion CD.
Another source for designs is Stock Photography sources such as ThinkStock:
Just google henna design templates and you will find all kinds of them. Trace the design with a little gel food coloring and then apply to the cake if you don't want to do them free hand. Good luck.