About 2N output (NPN), why the two outs connect to DC12~24V?

It appears that each output is driven low (ground) by a NPN transistor and driven high (+12 ~24 Volts) by a PNP transistor. I'm guessing that this is some sort of optical sensor where when light beam is blocked the output goes low and the output goes high when the beam is not blocked. ( The output could go high when the light is blocked and low when its not blocked)

To use the 2N output (low) you use the +12~24 volt line and the low output to drive some indicator/ circuit when the light beam is blocked
The 2P output (high) is used withe ground to drive some indicator/circuit of the opposite condition I.E. that the light beam is not blocked

Without knowing what the part is, impossible to answer your question. The information you gave is basically a box with terminals.

The outputs are probably open collector outputs. Read the specs and typical circuit operation instructions to find out.
What is the mfgr and part number?

You could at least show us the complete spec or tell us what this is.

However, i suspect they are not connected directly, but "out1" and "out2" are loads of some sort, perhaps a NPN transistor.

But I'd contact the manufacturer for more info, as all I can do is guess.