This is a mallsai. One you might buy in a department store. It has glued on rocks and moss. If you buy one of these the first thing to do is get the glued rocks off the surface. If you have an outdoor tree fill in the void, left from the glued rocks,with a quality bonsai soil. If you have an indoor tree you could go ahead and repot. The actual best time to repot is in the spring. Once you feel comfortable and can see a bonsai in your little tree you could start trimming. Check the links page for more help.

This is the same tree after repotting and pruning.