@shahryarjb If I understand you correctly then this code should help you:
categories # here you have root list from your gist
|> Enum.find(& &1.seo_alias_link == "jsjsjs") # here you have list element
|> Map.fetch!(:cms_post) # here you are fetching sub-list from element
|> Enum.map(& &1.title) # finally here you are getting title for all elements
