Where should I save/invest my NS income? I already have 10K in Singlife. Any advice?

Aside from SingLife, you can consider checking out Dash-Etiqa (2% for first-year) or Elastiq (1.8%). These are all guaranteed returns plan that is good if you are risk-averse or the money is meant for school fees etc.

You can consider investments such as robo advisors. This constitute 25% of my wealth and it provides a good entry point for investment as they have good commentary and explanation/Breakdown for your savings.

What I did when I was in NS was to start investing in my learning.

More specifically, the mindsets needed and the technical skills to learn how to invest well. Through picking great companies and investing in them when it was undervalued.

That way, I was able to utilize my NS income and grow it over time.

Not only that, after NS, I already had the experience on stock investing so I have an early start as opposed to others who don't.

It was also in NS when I start writing my blog on my investment thought processes. Do check it out and feel free to ask me any questions :)