ok! I figured it out myself...

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EDIT: what I wanted and how is done.

first I get the spin values for the object:

iObjectSpin(OBJ_OBJECT,object_spin);

that giveme, as the instructions clearly say and my dead brain couldnt understand... the axis of rotation where the object is spining and the rotation speed.

so, I want to reproduce it using a force, and need to position and setup that force correctly; first, I need a quartenion:

iQuaternionLookAt(quaternion_spin,object_spin,Vector3(0,1,0));

and the location of the spining object:

iObjectLocation(OBJ_OBJECT,object_location);

now lets position the force:

iObjectPositionReset(OBJ_FORCE,quaternion_spin,object_location);

set the intensity: (*)

OUT_FORCE=iVectorLengthSq(carspin);

and start it!

iObjectStart(OBJ_FORCE);

look mum, is spining!

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(*)
this is a little detail:
instructions say this value that iobjectspin give me is rotation speed (spin), in degrees per second so the fact that I use iVectorLengthSq to set the force intensity is a very pulled out of my arse thing... I just used that because, at naked eye, the reproduced spining looks almost acurate compared with the original one... logic tell me this, if possible, would requiere another formula. but at that point I didnt care anymore because the main subject was solved.