Is the billing export dataset is created per billing account or per project ?
You will have one dataset for the billing account, and it will contain info for all projects attached to that billing account.
You have a choice of the two options you mentioned in your question. If you navigate to the budgets and alerts option in the menu on the left, click on Trial Budget (or however you named it during the lesson). Under the name field, you can select a billing account or project only. This allows you to monitor a project’s expenditure on it own, or your entire account including all projects linked to the account.
One billing account can have many projects, so you can create a bigquery dataset on any of these projects and export billing to it. In the lab, the instructor creates a new project linked to the same billing account, and a bigquery dataset on this new project. You can create a bigquery dataset on the any project and export billing to it, a exclusively project for is not necessary but in many cases can be a good practice.
In my lab, under "Scope" of Budgets & Alerts for Trial Budget — I only see projects, not the billing account created earlier. Did I miss something?
Treat billing account as your Organization and projects as the departments or BU who account for the different budgets. For the Billing, it is not related to any department and should be in the Organization level cost. So i guess it is the real scenario in the practice.
One dataset for all project. You can check the details from BigQuery. You can also do SQL query against it.
Also, you can export the BigQuery to Google Data Studio to set up charts and see everything important to you in charts on one page.