Which are some of the best sites to learn coding & brush up computer skills?

TRY ALISON.COM 

they are the best and they are cirtifid...............thanks.

I can't tell you, because of no the publicity for these sites

But there are many of sites learn coding and brush up computer skills

Every site is good and different .I dont think there is one stop solution for this.You should start read

Blogs,forums,pdfs, guides watch video tutorials and presentations.And the most important is you should be curious and doubt full.

there are many professional websites you can learn from,, here are some that I have used: 

http://www.programmr.com/  for programming 

and https://www.edx.org/course  for free courses in many subjects including Computer Science and some programming languages. 

www.w3schools.com