[anderspetersson]

What is scaling to you? I will assume that scaling means keeping up with increasing load on servers.

The number of different scaling problems are about the same number that startups having problems with scaling. It's a different thing for every company.

You should probably specialise in a tech that many startups use and learn how to deal with high load on that service. Learning this takes experience, gain that experience by working/consulting/running you own startup using the tech you want to specialise in.

When you feel comfortable with one tech, learn another, repeat.

When you have enough tools in your belt you could apply to a senior position at a fast growing company.