I know answer to your question cannot be unique or acceptable for all. But I want to share some links I get redirected most of the time while looking for solution to my problems.
- Official documentation is at beginning phase as Magento 2 but it is getting better everyday.
- Alan Storm is the best magento blog writer I have ever seen.
- Inchoo is consistent at it's blog publishment.
- Mageplaza is good place to learn magento 2.
- Mukesh Chapagain is outstanding nepali blog writer.
- Cuong PHP is new youtube channel but excellent if it comes to magento 2 coding guide I have found till now.
I wil come back to add more good links when I encounter them. Thank You.