How can I add a second business to my personal business account. I am a partner in a second business for whom I do the bookkeeping. Solutions?

One QBO account is for one company file. You may utilize the Class feature to manage branches/divisions. Otherwise, you should open a second QBO account. You may use the same email address to manage multi QBO accounts.

https://quickbooks.grsm.io/Canada

Another option, consider having QB Desktop with a single license to manage multi company files. Deploy a private cloud if required.

Hi gailfreelancer20. I'm happy to learn you're using QuickBooks to streamline your business and manage your business with ease. The good thing about using QuickBooks with multiple accounts is that you can use one email address or user ID to access your accounts. I encourage you to check out this helpful article which shows you how to: 

Sign in to multiple QuickBooks Online companies with one user ID. 

Let me know if you have questions after reviewing the article. I'm here to help get you on track so you can get ahead with your bookkeeping. I'll be on standbdy.