Let's suppose you have project1 and project2 and you've never shared any dataset from project1 with project2. When you first share a dataset from project1 with project2 the dataset will not be shown automatically. For that you need to follow the following steps.
- Go to the BQ Console
- Click on +Add Data just above the search bar.
- Click on Pin a Project.
- Enter the project ID and click on PIN
After that every dataset inside project1 that you share with project2 will be automatically shown.