Hi Rasmus,
Greetings from Syncfusion Support.
Based on the requirement, we have prepared the below sample for week number template by making use of renderCell event like below,
onRenderCell(args):void{
if (args.elementType === 'emptyCells') {
let weekNumber = args.element.querySelector('.e-week-number span').innerText;
args.element.querySelector('.e-week-number span').innerText = "Week "+ weekNumber;
}
}
Kindly try the above sample and revert us for further assistance.
Regards,
Vengatesh