When people ask a question about one item in a chart, the answer can never be entirely accurate because you aren't considering the whole chart. That said, you can't just look at the sign and house as if the node is a planet and come up with its meaning. So if you are truly serious about knowing the meaning of your node, it's best to post your entire chart or birth date, birth time and birth city/country, because you might get more satisfying answers. The nodes work together - as opposites - because something of Sagittarius (in this case) needs to be balanced by new Gemini energy.
Generally, we look to the sign of the south node for the kind of energy of the past life. We look to the house for the kind of experience the person had. We look to the rulers of the sign the nodes are in for further information about the nodes. With the south node, we have skills and we have a wound to heal. So we look at negative Sagittarius energy here for the wound and the positive Sagittarius energy for earned skill set or qualities.
Sagittarius negative can be judgemental without even realizing it. It can be overly optimistic and then disappointed with failure because the goals were unrealistic in the first place. Sag can high exceeding high standards - which can be good to a point, but bad when one can't get what one really wants - because the standards are too high - too impossible to reach or find. Sag can be very enthused about something but have low follow through because it has so many interests. It can go from one thing to another thing and not finish anything. It makes conclusion based upon experience that aren't necessarily true, even if Sag believes it. Sag loves to be right and often thinks it is, even when it sometimes isn't. Sag sees things often in black and white - either / or - and doesn't see the shades of gray or other bright colors vying for attention. It loves to learn and grow, expand, and compete. Depending upon aspects from other planets - the Sag south node can be changed in quality and character - as well as where Jupiter is in the chart and its sign. So, this isn't written in blood, but is a place to start.
The Gemini north node helps a person look at the details. If a Sag SN is looking at the big picture only but doesn't know exactly how to achieve his goals, Gemini can help break it all down into steps. Gemini will consider everything while Sag like to think big and either/or terms. Gemini will take a long time to conclude something, a good balance for Sag. Gemini is more flexible, and eager to find the true through looking at details. Sag likes to find the truth too, but negative Sag will make conclusions and stick by them even when there is new information. Gemini thinks more, has more conversations and resists the temptation to make closing remarks. Sag will argue his point until blue in the face. Sag makes the better lawyer.
6th house will be about work and service, health, pets, perfectionism, science, doctors and nurses, aunts and uncles - it's a lot of things. If a person with SN there has an unhealthy diet, that speaks of negative health energy. It's still health. That would be expected even as a real possibility with a SN in 6th with other indicators. SN always speaks of some negativity.
12th house NN will always be saying, it's time to let go, release, let God - it's time not to expect perfection. It's time to relax a bit and not work so hard. It's time to attend to spiritual things - mediation.
Whole books are written about the nodes if you really want to make a study of it. But it's impossible to be definitive without looking at the whole chart - so don't conclude anything by what anyone says here on this forum. It's too complex to talk about briefly.