Nagarjuna is in Tibetan klu sgrub, sometimes also klu grub. We should actually say Master Nagarjuna, in monasteries and otherwise in the Tibetan culture you always provide an important teacher with a honorific title.
klu is naga in Sanskrit, these underwater beings that are actually quite intelligent, but still classified as animals. sgrub here means become, attain, and so on, so the rough translation is "born of the Nagas". Master Nagarjuna was definitely not a naga. Rather according to tradition he was invited to the naga realm to teach, and he found Perfection of Wisdom texts stored away while they were lost in the rest of the world. So he took these texts back and started teaching the context.
If you nicely ask a Tibetan lama the location where Master Nagarjuna descended to the naga realm, they might tell you.
Anyway, if you do internet searches you should find plenty of information about Master Nagarjuna. One option is to look at the dharmadictionary entry for a starting point to look at more information and Tibetan terms and words related to Nagarjuna.