Given a JSON file named data.json

{
  "name": "Matt",
  "job": "Engineer"
}

You can output the keys and values using the following

jq -r 'to_entries|map("\(.key)=\(.value|tostring)")|.[]' data.json > file.txt

file.txt contains

name=Matt
job=Engineer

You can upper case the key, by piping ascii_upcase to .key

jq -r 'to_entries|map("\(.key|ascii_upcase)=\(.value|tostring)")|.[]' data.json > file.txt

file.txt now contains

NAME=Matt
JOB=Engineer

You can also prepend text to the keys as well, here we’ll prepend WOW_ to each key

jq -r 'to_entries|map("WOW_\(.key|ascii_upcase)=\(.value|tostring)")|.[]' data.json > file.txt

file.txt now contains

WOW_NAME=Matt
WOW_JOB=Engineer