A metal ion with a net + 1 charge has ten electrons in the 3d subshell. How do I identify the metal?

First off, the + 1 charge means that the metal has lost an electron.

To identify the metal, we have to know the total number of electrons in the 3d sub shell.

Total number of electrons = 1 + 10 = 11

This metal belongs to the fourth period in the periodic table (that's where transition metals begin to occur).

This means that the 11th metal in this period is the metal. That happends to be Copper.