Does Craft CMS support these features? I am evaluating different CMS. I need to know if Craft CMS supports these features:


Preview function for different devices, screen sizes and screen configurations(portrait/landscape)
Is it possible to publish only a subset of my website?
Is lazy loading supported? E.g. loading images on scrollto?
Does a frontend created with Craft CMS use much .js code? Can I minimize the amount of .js code (for performance reasons)?
Is mobile first approach supported?
Are URLs SEO-friendly?
Can I integrate Onsite-Banners from external Ad servers?
Does the cms contain Digital Asset Management?
Which media file types are supported?
Is there any REST API provided?
Does the CMS internal search engine support synonyms and how about the error tolerance?
Can I login to the CMS on mobile devices? Do I have good usability when doing so?
Do I upload high resolution images and later on these are generated and maybe compressed for target devices?
Preview function for different devices, screen sizes and screen
  configurations(portrait/landscape)


Yes it has live preview. However this isn't per device. You can open the entry with a secret url and then user your browser tools to check different devices


  Is it possible to publish only a subset of my website?


Yes, each entry can be turned on or off


  Is lazy loading supported? E.g. loading images on scrollto? Does a
  frontend created with Craft CMS use much .js code? Can I minimize the
  amount of .js code (for performance reasons)? Is mobile first approach
  supported? Are URLs SEO-friendly?


Yes, it's all how you code it. You can do whatever you want. Craft makes no assumptions or requirements


  Can I integrate Onsite-Banners from external Ad servers?


Yes code as you want


  Does the cms contain Digital Asset Management? Which media file types
  are supported?


Yes, full list here: 


  Is there any REST API provided? Does the CMS internal search engine
  support synonyms and how about the error tolerance?


I'm not sure


  Can I login to the CMS on mobile devices? Do I have good usability
  when doing so?


Yes you do. I've done this myself and it was easy to move around


  Do I upload high resolution images and later on these are generated
  and maybe compressed for target devices?


Yes you can and then you can set transforms to crop/resize/compress as you want. Targetting per device that all depends on your html.