I'm a little confused about this myself. I assumed it was plural - two socks, two shoes. But they accept "the sock is in the shoe," so I guess it can be singular as well? I thought you had to say "half sock" to make it singular. Would you have to say "A fél zokni a fél cipőben van"?
If you're just talking about a pair of socks or shoes, then no, you don't use the plural. Things that come in pairs and are plural in English are referred to in the singular in Hungarian. However, I don't know whether there are situations where zoknik, etc, would be appropriate or necessary. A more fluent speaker than I am will have to answer that one.