Where does views's template files get saved?
Where should I place any view template so that it can effect all views
  of specific content type like "Article".


While you can do this with nodes, I don't believe it's possible on views to affect all views of x content type. As you can see in FILTERS, there is a Type filter (=Article). It's just a filter.

The best option you have is to make it affect a specific view name and a view display. 

EX: views-view-grid--[view-name].html.twig

if you want to specify a display then views-view-grid--[view-name]--[machine-name].html.twig

Then you copy the code from core's views-view-grid.html and paste it on your template file and modify as you wish.  

If you want to alter fields, then use views-view-fields--[view-name]--[machine-name].html.twig

You place your custom template files in /themes/[Your Theme]/templates folder.