You should have a small tab at the bottom left of your screen that has "Preview" and another that says "Output". If you hit the X in the preview pane and it shows up and is just blank, hit the "Preview" eye at the top on the menu bar and that should work.
You don't have Preview at the top showing because you aren't focused on a job...so if you expand the jobs and highlight one you'd get that option showing back at the top...if not close and reopen workbench.
I'd try to close/reopen workbench if that doesn't work.
If all else fails, think about what version of workbench you're on. I can't remember problems with older versions, but I always see Preview/Output in mine..so it may be something up with the version you are on....but that is just a guess.
it was there this morning but i accidentally clicked on close on that tab
I tried to close and re-open workbench, didn't work.
preview button works when i focus on a job but it doesn't show the preview or the ouput even when i click on preview or run.
my workbench version is 4.62.6715.32090