The magnolia trees that I have trimmed here in Florida, USA, have a somewhat bitter smell and taste (when some of the sawdust falls into my mouth). I would guess that it would have a combination of a bitter and floral smoke flavor. I would try to find out which species of magnolia you might have, then do some research as to potential toxicity. If everything looks good, then do a test burn of a small dry piece. If the smoke smells good, then smoke a single piece of chicken breast to evaluate the flavor.
Personally, for all of the unknowns, I would just burn that wood up in a campfire and find a known good smokewood.
18.5 WSM, Green Weber Genesis320, Cast iron firepit(w/grill), and a Copper Weber 22" OTS