jekyll: 3.9.3
liquid: 4.0.4
my.hash: {"key1":"value for key1","key2":"value for key2","key3":"value for key3","key4":"value for key4"}
my.list: ["key4","key3","key2","key1"]

{{ page.my.hash["key1"] }}

hash["key1"]: value for key1

{{ page.my.hash[page.my.list.first] }}

hash[list.first]: value for key4

{{ page.my.hash[page.my.list[0]] }}

hash[list[0]]:

val = page.my.hash[page.my.list[0]]; {{ val }}

hash[list[0]] via assign:

key = page.my.list[0]; {{ page.my.hash[key] }}

hash[key] with key = list[0]: value for key4