Look at the right hand end of the line immediately above the e-mails, where you're seeing column headings such as "Subject" and "Date". You should see a divided rectangle with a down arrow - click on it & tick the columns you want to see, presumably "Recipient" and "From" or "Reset columns to default".
You can also get there by right clicking on one of the existing column headings.
Another possibility is you've done something that "minimises" the column so that it's still there but dragged across to minimum size - look carefully for column dividers if you think this might be the case.