Converting Json to XML usin JS service in thingworx

I numbered the issues your code had

try {
	// 1. cannot name variable JSON - as JSON object already exists
	// 2. json string must be a valid json object, having "" around attribute names
	let json = '{"College":{"entry": [{"Student": "shiv", "Roll_No": 12},{"Student": "yadav","Roll_No": 56}]}}';
	// 3. don't use let for result variable when used in a block (here try,catch). the variable will only exist in the block
	// 4. when you pass only a string, it will not be interpreted as an object. need to parse the string first
 result = OBJtoXML(JSON.parse(json));
} catch (e) {
	logger.error("jsCodeToConvertJsonToXml: error is " + e + " in linenumber " + e.lineNumber);
	throw e;
}

function OBJtoXML(obj) {
	var xml = '';
	for (var prop in obj) {
		xml += obj[prop] instanceof Array ? '' : "<" + prop + ">";
		if (obj[prop] instanceof Array) {
			for (var array in obj[prop]) {
				xml += "<" + prop + ">";
				xml += OBJtoXML(new Object(obj[prop][array]));
				xml += "</" + prop + ">";
			}
		} else if (typeof obj[prop] == "object") {
			xml += OBJtoXML(new Object(obj[prop]));
		} else {
			xml += obj[prop];
		}
		xml += obj[prop] instanceof Array ? '' : "</" + prop + ">";
	}
	xml = xml.replace(/<\/?[0-9]{1,}>/g, '');
	return xml;
}

Returns:

<College><entry><Student>shiv</Student><Roll_No>12</Roll_No></entry><entry><Student>yadav</Student><Roll_No>56</Roll_No></entry></College>

Also, next time please use the

feature for source code.