Hello there, @Michelle C.

Adding the SKU column on a purchase order is done by a few steps. To get started, let's turn on the SKU feature from the Products and services section.

Here's how:

1. Click the Gear icon, then click Account and Settings.
2. Select the Sales tab and go to the Products and Services section.
3. Mark the Show SKU column box.
4. Click Save and hit Done.

Once done, you can enable the SKU option on the Standard template. I'll guide you how. 

1. Click the Gear icon, then select Custom Form Styles.
2. Locate the Standard or Master template. 
3. Click Edit.
4. Go to the Content tab and click the middle part of the template.
5. Select the SKU option.
6. Hit Done.
7. This will show the SKU column on your purchase order.

I've provided a screenshot below. 

You can get more details in the following resources below:

• Customize your invoices, estimates, and sales receipts in QuickBooks Online.
• Add your product’s name, SKU, and category.

If you have additional questions, I'm just around. You can tap me, and I'll get back to you as soon as I can.