I was brought up as a Jehovah’s Witness. There are no “membership fees” and neither is a collection plate passed around at meetings. However, there are contribution boxes at the back of the Kingdom Hall and this is where Witnesses place their financial donations. Witnesses voluntarily contribute towards the running costs of the Kingdom Hall and the worldwide activities of the organization. It is out of such contributions that the running costs for national branch offices and the headquarters in the U.S.A. are met. These costs are considerable, even though the full-time workers receive only their board and lodgings and a small monthly allowance.
During the 2018 service year, Jehovah’s Witnesses spent over $214 million in caring for special pioneers, missionaries, and circuit overseers in their field service assignments. Worldwide, a total of 20,331 ordained ministers staff the branch facilities. All are members of the Worldwide Order of Special Full-Time Servants of Jehovah’s Witnesses. Source: https://www.jw.org/en/publications/books/2018-service-year-report/2018-grand-totals/
When I was a Witness we had to pay for the literature that we used when going from door to door. Back then, we sold the Watchtower and Awake magazines to interested persons. Pioneers (those who devoted part of their time to the preaching activity) would make a small mark-up on the sale of literature in order to help them cover their costs. Special Pioneers (who were full-time in the ministry) also received a monthly allowance from the Society so they could pay for rent and food. To the best of my knowledge, this was the case since the 1930’s (when my parents became Witnesses).
Changes were introduced when the Society claimed income tax relief on the basis that they were providing free education. It became illegal to sell the literature – it had to be given away free of charge. But the Witnesses still pay for the literature they order and then give away.
As for Assemblies and Conventions, the costs of hiring large halls or stadiums and the other expenses incurred in hosting such gatherings used to be met by the congregations in the particular circuit or district in which they were held. Since 5 May 2014 changes to congregational financial commitments were introduced. All congregations (world-wide) were instructed that they had to pool their resources to support the construction of “theocratic facilities” wherever they are needed. That involved each congregation resolving (committing) to make a monthly contribution to H.Q. in order to pay for Kingdom Hall and Assembly Hall construction work worldwide.
“Elders should review this resolution annually in May to ensure the amount is what the congregation is realistically able to donate on a monthly basis. For example, there may be a significant increase or decrease in the number of publishers in the congregation, or the local economic conditions may appreciably improve or deteriorate, thus affecting the amount that the congregation can reasonably contribute. If necessary, the elders may take a new financial survey, as described above, to determine whether the resolved monthly contribution to Kingdom Hall and Assembly Hall construction worldwide should be adjusted for the coming year.” – March 29, 2014 BOE letter, page 2
However, no collections have ever been made in either a Kingdom Hall or at a regional, national or international convention. All costs are borne by the Witnesses who make financial donations to the organization, whether by placing money in the boxes at the back of the Kingdom Hall, or by monthly electronic contributions or by bequeathing their money/property/stocks/bonds/shares in a will. When my father died at the end of 1999, he left everything he had to the organization (with the exception of a small life-assurance policy to cover the costs of his cremation). Such was his faith and commitment to the organization.
Each congregation is therefore committed to making a monthly financial contribution to support the world-wide preaching work. The individual members of each congregation are likewise committed to ensuring those monthly payments are met. Witnesses may not be asked to tithe their income, but they are expected to pay for every cost incurred locally as well as for the global overheads.
For what it's worth, the evangelical church I attend doesn't make any collections either, nor does it insist members tithe their income. We all give what we can, freely and cheerfully.