I've never had a need to try any lubricant on my sebenzas. Once they'd broken in I found that they were as smooth opening as I could imagine. That and the fact that lubricant + lint/grit/schmutz = crud and then the need for more frequent cleanings.
If you do lube it, go washer to tang side only. As far as I know, that's the only movement point.
And given that it's only subject to thumb generated forces, I'd guess that whatever lubricant you use is just a matter of personal preference. Kinda like you can lube a door hinge with wd40, grease, butter; it doesn't matter... it's still as lubed as necessary. On an engine, or even a firearm you can start getting picky, but a pocket knife is going to be well enough lubed if you even wiped the tang on your forehead before reassembling.
If it's cutting a lot of food it wouldn't hurt to go with a food-safe product, but the amount of contamination would be negligible either way. Odour might be a consideration if you don't want a pocket smelling like wd40 if you overdo it.