Can I add "still" on both sentences below? why?

'Still' is redundant and confusing.

Check your other question. I've answered it at length.

You can say either version of the sentences quoted. Whichever version you use it will be grammatical.

1. The first one means that you are part way through a journey and you want to know how much longer it will still take. Reply.... 'It will take about an hour.'

2. the second one is asking the same question but needs a more specific answer. Reply.... 'it will still take another hour '.

How long does it currently take to get to California?
Correct.

Does it still take (blank hours) to get to California?
Correct.

The other ways you have written it show that its written by a young person or a foreigner. How long does it still take... is wrong.

I believe that you can use both good luck