Finder won’t launch after Mojave upgrade ( high system cpu )

When you see a process in parentheses/brackets it means that ps could not determine its command (which appear in the CMD column). This might explain why you don't see it in the Activity Monitor.

You can restart Finder also outside a shell. Just click on the Apple symbol in the top left corner of the MacOS task bar, click on Force Quit and select Finder (usually at the bottom)

Generally, I find top more convenient than ps, but I think both should work equally fine.

As far as I am concerned kernel_task was always trying to tell me that the computer is running hot. It seems to be a strange countermeasure which occupies the CPU with a low energy No-Op task which prevents it from doing "hotter" things. So you should be looking for that "other" process eating up the rest of your CPU time.

However I noticed very high CPU usage of Safari ever since I update do Yosemite 10.10.4. The browser visibly (in Activity Monitor) starts several processes now and two of them (Safari Networking and nsurlstoraged) routinely take up a lot of CPU, especially Safari Networking often takes more than 50% of one CPU. It seems to be less constant now, so maybe there is some "trickle down" effect on this one.