As the benefit of this membership can be received by any number of Awards, the cost cannot be allocated to a single Award. The cost of membership should be billed to either department funds or a discretionary budget.

If the traveler was a presenter, ideally a copy of the agenda that lists the traveler and the name of their presentation would be provided. This can be obtained from the traveler, a conference website, or other source. Alternative documentation would be a copy of the presentation (or at least the cover sheet, if the presentation is long) that includes the presentation title and the name of the presenter.

It is the expectation that these funds are for the benefit of the University, rather than the individual PI. The Dean/Director/Chair has the authority to direct the use of the funds at the request of an individual PI.

Documentation of receipt of the package in Workday is evidence the item was received. Please see information on "System Receiving for Order" from UW Procurement for more information. System Receiving for Orders | Procurement Services

No, this is not an allowable cost unless there is specific written sponsor approval for this cost. 

Yes, provided that prior sponsor approval has been obtained in writing, the costs are paid in accordance with University policy, and that UW policy is consistently applied to all similarly situated employees.