Looks like somebody has buggered with it before you bought it. There ought to be a head with a fitting for a 6-sided hex key on the end of that rod--as I look at your photo I see damage to the underside of the soundboard under the fretboard as well as to the area where the head of the truss-rod ought to be, and the metal rod itself appears to show evidence of having had the head broken off. I do not believe that there was ever a nut on that rod, only a head that appears to now be broken off.
There is one other possibility.....I do know that many custom shops are installing a non-adjustable graphite rod into the necks of some of their classical guitars to reinforce the neck and hopefully avoid any movement of the neck in the future. However, this is a very high $$ custom shop option and to my knowledge Washburn does not do this.....but I could be wrong.
I'd suggest a call/email to Washburn's customer service department. Since you bought the guitar used, Washburn will not offer any warranty service, but they may be able to shed some light on the issue and at least you will know where you stand.
Any chance the seller might confess to his previous transgressions and refund your $$???
Good luck, please keep us posted. I have seen very few classicals with adjustable truss-rods in their necks and own a C124SW, a slightly more expensive Washburn classical produced at about the same time as your C104SCE. Right now it is almost 1,000 miles from me so I cannot look into the body to see if it has any adjustment mechanism, but I would doubt it.
YerDugliness, Esq./Post No Bills
Guitar Playin' FOOL, retired & attempting to age disgracefully!!
Washburns: WD32S, WD32SW. D61SW, and C124SW
Other fine guitars by Breedlove (custom shop Revival Series 000), Darren Hippner (#506), Takamini (2005 LTD), Epiphone Masterbilt (AJ500RC), and Yamaha (G231-II)