I tried to find this from the books, but couldn't so far...

Usually one wants to inflict as much as possible, but there are times when disabling someone is enough instead of killing. With a gun it's bit difficult, but with a melee weapon or unarmed combat it's not that difficult instead of doing a killing blow, just do a stunning blow. This will of course on the case of a bladed weapon reduce the AP (if any) and damage value to a simple club, but in case of clubs (and alike) and unarmed, one can just do a not-so-critical punch. On normal unarmed the damage is stun, but if one has a pair of hardliner gloves or bone lacing, can or can one not inflict stun damage?

I'd say yes, stun is perfectly doable with almost all melee "weapons", but couldn't with some searching find a ruling that would say one or the other.

I recall that you could always choose physical or stun with melee...but you took some kind of minus to hit with say, the flat of your sword.

I think Bone Lacing folks can do Physical if they want, but don't have to.

in SR3 there was only the option of instead of doing stun trying to do physical damage with things like bonelace . . it meant you did not do STR+2M Stun Damage, but STR+2/2M Physical Damage for example . . the only thing that really let you chose what kind of damage you wanted to do was killing hands of adepts. and as far as i know, that never changed O.o

I remember that, actually. Someone with a 6 Strength and Titanium Bone Lacing would do 9M Stun unarmed, but 5(it did round up) M Physical.

In this one, i guess they half the strength already, so it's just a matter of choosing.