In his 6th house. Here the original question: my S.N. (which is in Saggitarius, in my 6th house) is conjunct his NN (in Sagittarius, in his 6th house). Alternatively, his South node (Gemini, 1st house) is conjunct my North Node (in Gemini, 1st house). His S.N. is conjunct my Chiron (in my 1st house) and that my S.N. is conjunct his Neptune, (in his 6th house).
About SN conjunct his Neptune (in his 6th house).
His Neptune conjunct your south node is important especially since Neptune is your ruler. Since south node also indicates past lives and when in such a close aspect, it brings the feeling of an old bond revived. Maybe he was your spiritual teacher or a healer in some past life. Maybe you were making music together. Maybe you had a joint pagan sect. The bond is very spiritual and it’s a deep inner knowingness that makes you feel that “he knows” without much need for explanations.
If Venus is conjunct the south node, it is a past-life lover and you share a haunting chemistry with them. The sun and the moon can indicate a parent; Jupiter, a teacher and so on.