This Commented CUE demonstrates how to use the built-in function encoding/json.Compact to transform a JSON file into a single line of JSON with all insignificant whitespace removed.

file.cue
package example

import "encoding/json"

compact: json.Compact(json.Marshal(input))

// The contents of data.json is placed here by
// the -l parameter.
input: _
data.json
{
    "a": 1,
    "b": {
        "c": "two",
        "d": 3.0
    },
    "e": false,
    "f": [
        4,
        5.0,
        "A\nMulti\nLine\nString"
    ]
}
TERMINAL
$ cue export file.cue -l input: data.json -e compact --out text
{"a":1,"b":{"c":"two","d":3.0},"e":false,"f":[4,5.0,"A\nMulti\nLine\nString"]}