how to write a javascript stored procedure in azure cosmo db to return the data from sql apis?

You can try something like this:

function getItems(category,fieldName) {
    var collection = getContext().getCollection();

    var query = 'SELECT distinct cx.ID, cxa.FieldValue as PartNo, cx.TransactionDate, cx.TransactionStatus ' +
                'FROM c ' +
                'JOIN cx in c.File.Transactions ' +
                'JOIN cxa in cx.AppDetails ' +
                'JOIN ' +
                '( ' +
                    'SELECT cx2.ID, cxa2.FieldValue as PartNo, max(cx2.TransactionDate) as TransactionDate ' +
                    'FROM c ' +
                    'JOIN cx2 in c.File.Transactions ' +
                    'JOIN cxa2 in cx2.AppDetails ' +
                    'WHERE c.File.Category= @Category and cxa2.FieldName = @FieldName ' +
                    'GROUP BY cx2.ID,cxa2.FieldValue ' +
                ') B ' + 
                'WHERE c.File.Category= @Category  and cxa.FieldName = @FieldName';

    var filterQuery =
    {
        'query' : query,
        'parameters' : [{'name':'@Category', 'value':category},{'name':'@FieldName', 'value':fieldName}] 
    };

    var isAccepted = collection.queryDocuments(
        collection.getSelfLink(),
        filterQuery,
    function (err, feed, options) {
        if (err) throw err;

        if (!feed || !feed.length) {
            var response = getContext().getResponse();
            response.setBody('no docs found');
        }
        else {
            var response = getContext().getResponse();
            var body = feed;
            response.setBody(JSON.stringify(body));
        }
    });

    if (!isAccepted) throw new Error('The query was not accepted by the server.');
}

By the way, when you invoke stored procedure, you need to pass partition key value. And you can only get the data from this partition. You can refer to this doc and this.