We have a 2 story older home of which we want to remove a 11 foot, 2 inch span. I understand we need to build a temporary wall approximately 3 feet from this wall for support, however we have dropped the ceiling in this room and the 2x4s are only attached to the existing old walls not to the joists. Will this be enough support for a temporary wall and if not what can we do without tearing out the new ceiling, also what size header and jack posts do we need? We can access the wall between the floor joists and the new ceiling from the exterior of the house.

first off- do not attempt this without a qualified expert on site. Getting information online is not reliable enough for you to stake your life on. That being said - if you are just fishing for info- the original ceiling joists must be directly supported by your temp wall. You should have a double top plate and each stud should be placed directly under each joists. If you dropped ceiling is in the way I suggest installing a double 2 x 6 header to the underside of your original ceiling joists, then install double studs at periodic locations through your dropped ceiling. Install a double bottom plate on the floor to disburse the weight. I personally build my temp walls no more than 24" from wall being removed. That's usually more than enough room to work. Again***** Please do not attempt without someone qualified. The new header (beam) for an 11' span should be spec'd by an engineer. There are too many unanswered factors the this depends on. What's above( bedroom , bathroom- if bath a bif tub- lots of tile- what's your roof load-do you get snow?) I'm not asking for answers- just letting you know what this involves. Call a professional.
good luck