I have money in a 50/50 partnership with a friend who is managing it. Is zakat obligatory on it?

If your share of the money reaches the [nisab] threshold—by combining it with other zakatable funds—then you must pay zakat on this money and its profit upon the completion of a full Hijri year from the time you acquired it, provided that it reaches the nisab at that time, either by itself or by adding it to what preceded it. If you purchase trade goods with it, then the [hawl] (annual cycle) for trade is built upon the previous hawl, as long as the capital remains at the nisab.