@JR, you can load the assembly record just like you did the work order and then add it to the renderer with something like renderer.addRecord('assembly, your assembly record). Then reference the record in your template with ${assembly.something}

@jarens, i added the following to my suitelet, and it worked! thanks much!!!

var workorderRecord = nlapiLoadRecord('workorder', id);      var assemblyItem = workorderRecord.getFieldValue('assemblyitem')
    var assemblyRecord = nlapiLoadRecord('assemblyitem', assemblyItem);
    renderer.addRecord('record', workorderRecord);
    renderer.addRecord('assembly', assemblyRecord);