Slitherine

For a unit to have a flank support bonus, should the supporting unit just be on the flank of the attaqcking unit and slighly towards the target or on the flank of the target

Not quite sure what you are asking here.
What constitutes flank support in combat is pretty well set out in the rules, IIRC, don't have a copy with me to check at the moment.

Ok let's do it that way . In the rules it is not that pretty clear for me . Where should the supporting unit be

On the flank of the supported unit

on the flank of the assaulted unit

The supporting unit has to be on the flank and within a base depth of the friendly unit and the enemy has to be within the support area of the supporting unit. Support area is forward of the supporting units front line and also within one base width of its side edge.
Support area seems to be covered on page 51 under supporting fire. Also see diagrams on pages 52 & 53.
Those are the only references to support zone I can find

The supporting area for combat is the same as the support area for firing - as shown in the diagrams on pages 52 & 53