To extract `961438154596153411` from the json, pipe the file in `jq '.id'`
Example:
$ jq '.id' << EOF
{
"id": "961438154596153411",
"username": "testing",
"avatar": "a9000496add364b16af27e2f583a2e1e0f",
"discriminator": "1"
}
EOF
outputs
"961438154596153411"
If you want it without the quotes, use `-r` for raw data.
All togeather, to put that number into a bash variable, I'd do this:
$ id=$(curl random args "link" | jq -r ".id")
$ echo "$id"
961438154596153411