The general idea (but there are specifics) is for the 1065, through the K-1s, to inform the partners about their distributive shares of the partnership items that need to be reported separately to them so they will know where to put them on their 1040s, in turn because they might affect (change) the tax calculations for the partners.
I'd say take a look at section 702, and then reg. 1.702-1. They won't tell you in so many words what line to put the expenses on (and neither will I) nor what code to use (and neither will I), but they will enable you to figure out whether they fit into a class or item of partnership income, gain, loss, deduction, or credit described in subparagraphs (1) through (9) of reg. 1.702(a). If they do, then they needed to be reported separately to the partners, which brings us to your questions. We can't answer you, because we don't know enough about the nature of the expenses or, more to the point, the nature of the business and/or investment operations of partnership B.
Then you'd scan, and in some parts peruse, pages 30 near the bottom through somewhere on page 49 of the 1065 Instructions, even though hardly any of it is likely to apply but you never know, because those pages are all under a heading called
(Schedules K and K-1, Part
III, Except as Noted)
Sometimes we just have to read a lot of stuff, but it helps for the next time and the times thereafter.
Which reminds me - your OP asks about lines for deductions on partnership A, and my above response leapt to the interpretation that you must mean on Schedule K of the 1065 of partnership A. I got there by deduction from the clues you provided by your listing the line numbers.
Last edited by Nilodop
on 16-Mar-2019 8:03pm, edited 1 time in total.