From a layout based on RepairTicket, you can use Go To Related Records to pull up a found set of all related records in AssemblyLine.
You can sort these records to group them by Assembly and put fields from Assembly into a sub summary part to serve as a "sub header" above the listed parts. You can include fields from Assembly part in the body of such a report to provide more info--such as a name or description about each listed part.
Note that this is at least a two step process: GTRR, followed by a sort to group the records.
You will need to test this. I have encountered cases in older versions of FileMaker where you had to do more than one GTRR. In some cases, you had to do a GTRR to an intermediate table and layout based on that table followed by a second GTRR with the "match found set" option enabled before you got the desired found set. Hopefully, this is not necessary in your case and with FileMaker 15, but test to be sure.
I just posted again with a different approach. I am so confused and desperate for help on this.
What I really need is the last table shown (example in Excel) where I have every BUILD DETAIL for every row in the TAKEOFF DATA table.
Your other approach is confusing.
What I suggested here will work for what you want if what you want matches the design of the sample file that you provided.