Sorry for the late response. I ran a few tests from my end to check how exactly this path would look like. See the step-by-step below and let me know if something is not clear enough :)
I created this task for testing purposes, which is assigned to a user called "Flows Test" (which is actually a shared mailbox, but contains a related record in systemusers table):
I used this flow to navigate from the task until the user data:
For the List rows - Tasks, I'm retrieving all records from Project Tasks table, filtered by name. I just took the name to keep things simple, but you can use the project name and project bucket, as you mentioned in the previous message. Based on your description, you were able to access the project tasks in Power Automate, so this part of the process is not new:

Now let's access the Resource Assignments table, filtering the records by project task. For it, you will need to use the _msdyn_taskid_value in the Filter rows input (in green), to use a lookup reference to the msdyn_taskid column (the logical name of Project Task column in the Resource Assignments table). Still in the filter query, you must check if this property is equal to the msdyn_projecttaskid property retrieved by List rows- tasks, which corresponds to its GUID (in blue). Since I'm working with a single record, I hardcoded the array reference with the zero ([0]), but you could also implement this logic within an Apply to each to access the assigned users for many tasks:

In the image above there is also a Expanded Query (in red) referencing the Bookable Resource column (msdyn_bookableresourceid). This is a important step to avoid making an extra List rows in this flow. the expanded query basically retrieves the properties from a related record in another table (in this case, Bookable Resources), when you have a many-to-one relationship. As a consequence, Power Automate will retrieve all data from the record in the Resource Assignment table, and the data from the related Bookable Resource.
Now let's finally access the user properties. You can use a Get a row by ID action for it, since we have the user ID from the Bookable Resource data. Pass the expression outputs('List_rows_-_Resource_assignment')?['body/value'][0]['msdyn_bookableresourceid']['_userid_value'] as input, which corresponds to the user ID recorded in the Bookable Resource data (and retrieved in our Resource Assignment due to the expanded query):
At the end, I added a Compose just to print the values of the user full name and its email address. After running the flow, this is the output
Let me know if it works for you or if you need any additional help!
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