You should be able to feel bulges in her belly at around 2 weeks.
First feel a male or female who your sure is not pregnant to practice on and to compare with.
Place them on a table, hold them with your left(non dominant) hand with their heads pointing at your belly button.
Cup their abdomen/bellies/guts with the palm of your right hand and feel around. You can't damage a buck or non pregnant doe unless you pinch something tight. You will mostly feel intestines and maybe their bladder, you won't feel the liver, it is up under the ribs, or the kidneys, these are glued to last ribs close to the spine and are not floating around.
Practice being gentle and keeping the rabbit relaxed, you dont want a pregnant doe to wiggle or be so tense you can't feel anything or may apply too much pressure.
Now in a pregnant doe the uterus will have little grapes (size depends on the breed) that feel like tumors in her belly. Don't squish them or handle them roughly as they can be damaged.
Later in pregnancy her belly feels tight, as she is running out of room th there and you cannot squish her intestines at all.
Further reading
http://www.hlrsc.com/Articles/palpation.html