In the UK people normally pronounce it 'Van Goff' as Max said. Having just done a bit of research online the pronunciation recommended by the Oxford Dictionary for British English is apparently 'Van Gokh' (the end sound is the same as in 'loch') but despite that I don't think I've ever heard anyone ever pronounce it that way. It seems to be an attempt to make it sound more like the Dutch pronunciation which most British people just ignore lol. I've heard it pronounced by Americans as 'Van Goh' but which is the favoured form in the States, I'm not sure.

Since van Gogh was Dutch, the correct pronunciation of his name would be the Dutch way. Because you speak Arabic I believe you are able to pronounce the Dutch 'g'. I can recommend this video if you wish to try; https://www.youtube.com/watch?v=YrI2-bZ7wpc van = not like 'van' as in 'minivan' but like 'vahn', more sounding like 'dawn'. Gogh = 'gog', h is silent. With 2 g's of the video above~ However, because it's a difficult to pronounce name for English speaking people, 'van goh', 'van goff' or 'van gok' are completely fine as well.

English (UK): Van (like the vehicle) Goff Dutch: Fah-hHochh (kinda hard to write down) http://vocaroo.com/i/s1zg75TmMzwe England, Holland (my best effort haha), and what I think they say in America...

U.S. usage is Van Go. If someone used the others, though they are correct, it would be seen as pretentious here.