Tyres and tubes would be a good place to start, as Andre says there can be a huge difference. What do you have on it now?
Then before swapping components, consider what you have attached and if you need it, racks, pump, lock, lights, bags... when you come to lift it the less stuff on it the better so anything that doesn't need to be attached might be better off in an easily removable bag. Only then would I start looking at components. wheels might be a big one, but also a big job and expense, so I'd be inclined to leave alone. Saddle? If you have a kg of cowhide there, it might be time to look at alternatives. Bar ends? Crankset? There's a lot of weight difference in these, external bearing seem to be lighter, what have you? BB to match of course, and look at pedals at the same time. Then there's not much left, bars and seatpost, if they're the Thorn branded originals they're mid weight and durable, you might shave a couple of hundred grams off, but you might not want to. Likewise brakes, I assume V's? I've never considered the weight, there might be some saving.
I don't know what your frame weight is, this is the only part of your bike that isn't changeable, assuming you stick with the idea of the Rohloff. I did a quick google and found a review of a S&S coupled Nomad, bike weight 16.9kg frameset weight 3.8kg, maybe 3.5 without the S&S. This is what you're dealing with, this is the point I'd like to get across, if you build another bike up with a similar spec, you'll only be improving on that 3.5kg.
https://www.bikeradar.com/reviews/bikes/road-bikes/thorn-raven-nomad-ss-review/I've only considered your question in relation to lifting it, there may be other good reasons to choose a different bike.
