Know how google/bing/duckduckgo to find examples on how to code those problems and then apply those to their problem.

A little explaining:

15-20 years ago I was asked by someone on how to code to convert a decimal to hex (not in TSQL) and I was surprised he didn't know it. So I investigated a little and the best answer I got was:"I have to think about it". I considered it shocking that no one said me : give me 5 minutes (which I considered already a long time) and I give you the solution.

In those years, I think everything changed. I think it is more important to be able to find solutions on the internet (few had internet 15 years ago) that you can apply to your specific problem than to know directly how to code it.

I do agree that to be considered a TSQL expert (I do NOT consider myself a TSQL expert even if I am able to write complex TSQL selects that perform quite well), you should be able to write with ease a lot of those core TSQL.