How to create a custom markup for a views-block?
If you want to create custom markup/template for that particular view of content type then create file and name it as views-view-fields--[view-name]--page/block.html.twig and save it in template directory of your theme.

Now to get the variable just goto the content type -> manage fields. There you will find the machine names of fields. those are the variable you need to place in html structure like this 
{{ fields.field-machine-name.content }}
 Hope this helps :)