How to check signal waveform.

First you're probably doing a timing simulation, which means it's after synthesis, so temp would no exist because it gets synthesized out.

Second, even if doing a functional simulation, temp isn't doing anything. Your simulating 1111 - 1100. That is a constant. Note that this is not sequential code but parallel, so all things are happening at once. Basically the code will have a constant output of out1 getting 0011. There's no logic in the design.