O2 sensor placement

So I'm new to this whole "tuner" scene and this is my first
Honda project. I bought a new exaughst for it because the
one I bought it with is awful, won't even start, but it doesn't
have a catalytic converter just a resonator so I'm
wondering where I should place the downstream o2
sensor so it's not reading the same as the first and
throwing a code? I would assume after the resonator but
like I said this is my first project by myself so I'm not
completely sure. Also the idiot owner before me cut the
port for the second o2 so it's hard wired in currently and
am probably gonna do the same again or find a port off a
parts Civic and wire that in. Is that going to effect anything
if I do either of those?