the best thing to do.. is put it back in the ground.. AT THE PROPER PLANTING TIME FOR YOUR LOCALE!!!! right now... more leaves.. means more food production .. means more root growth.. which means success ... eventually.. you should remove all the suckers to one or two left ... it depends whether you want a tree.. or a shrub .... i would wait until spring.. to insure the old part is truly dead ... at that time... if it does not bud out.. once the new growth hardens off.. i would perform surgery ... and remove it .. probably within two to three inches of the new sprouts .... a picture would sure help make that decision ..... if it is the plain old variety .... your new sprouts should be just fine.. if it was some foo foo named cultivar ... and it has sprouted from below the graft... you will have a plant based on the root stock of the graft.. which may or may not be to your liking ... only time will tell ... unless you can ID the graft location ... trees, shrubs, and conifers are amazing .. in their ability to overcome just about anything.. when just provided just water .... go figure on that .... now.. lets discuss what possessed you to do this in the first place .... lol ... good luck ken

Check Bauhinia blakeana or other Bauhinia.

could be a young magnolia but It does look like a fig if you select 3-4 of the strongest branches and prune them at about 1ft from the soil, it will grow in a nice open habit...or select one and prune it at about 2ft, stake it and it will be more of a half standard style the whip should be pruned at about 1' as well, this will induce branching below the cut

If you are asking about lichens those are harmless. If you are asking about bacterial leaf spot that is an infestation. But to get rid of it you will have to find out for sure if that is what you have, then undertake a specifically targeted spray program. Targeted as in using the right chemical in the right concentration at the right times. Otherwise magnolias like better soil conditions than many other plants will put up with, if yours seems stunted or has poor yellowish leaf color try top dressing with composted manure. If it is a small specimen you can probably find enough of the product in bags at local retailers. A bigger job and it starts to become more economical to buy it in bulk. All the more so if you have a truck, can have the bulk product loaded into that instead of paying a bark and soil dealer to bring it out to your place in a bigger truck.