Hi, I'm wondering how to make a mould to achive something similar to the pic below.
First of all, is it possible to have it in one single mold?
Where would you place the parting planes and how many?Thanks!

Splitting it side-to-side is probably easiest - with a vertical fore and aft plane.  The outside faces of the plates will be open laminate and could have plates bonded to them.  It looks like there is some draft on the bottom face to help release. 

If you are only building one part and going to paint it it would be way easier to just make a shaped tube and fillet it to top and bottom plates and tape a few plies of material over.  Probably only makes sense to make a mold if you're building a bunch of them or want some cosmetic carbon look.  

That looks either post-painted or there was some gelcoat repair at the seam... what is it made of?