How do they extract the juice from the Noni fruit, in the relative commercial industry ?

Answer 1

Check out this web site.

http://www.trunoni.com/tree-to-bottle/7_page.htm

They tell how they make their Noni juice using a bladder press to squeeze the juice from the Noni fruit.

Answer 2

Morinda citrifolia, commonly known as Great morinda, Indian mulberry, Noni (from Hawaiian), Nono (in Tahiti), and Ach (in Hindi), is a shrub or small tree in the family Rubiaceae. Morinda citrifolia is native to Southeast Asia but has been extensively spread by man throughout India and into the Pacific islands as far as the islands of French Polynesian, of which Tahiti is the most prominent. It can also be found in parts of the West Indies.


you should read
Noni: The Complete Guide for Consumers and Growers. Permanent Agriculture Resources, 112. ISBN 0-9702544-6-6.
it's a good book