There is no such thing. Expressions cannot genmerate any layers or other items. That's what scripts would do. At best you could rig expressions that manipulate the transform properties, but you'd still have to duplictae the layers manually. Anyway, without better info nobody can tel lyou what you might actually need. Such unspecific questions are pretty useless.
Probably your best bet is to select the layer you want. Go to Edit > Copy with Property links. Then duplicate the layer and with it selected, go to Edit > Paste. This will create “live“ linked expressions from one layer to the other. Then you can just manually duplicate the layer till you have the number you need. Using Commd/Ctrl D to duplicate is very quick and easy :-)