How do I get v0 using superposition in this circuit?
No, you pick a single source to use in your 1st analysis and, for ALL the other sources, you make them short (voltages) or open (current). That's how superposition works for each source. Then you add the individual voltages derived for each \$V_O\$ to produce the final value of \$V_O\$.

In other words:

Use one source with the others disabled then step and repeat for each source: -