What is the ruling on working as a technical support specialist at eBay, and what is the ruling on owning shares in the company, knowing that it takes a percentage from sales transactions that may include forbidden goods?

There is no objection to your work as a technical support engineer at the aforementioned site, and it is permissible for you to own and benefit from the shares granted to you. If you strongly suspect that a portion of the profits is earned from unlawful means, then donate the percentage of this portion to the poor and needy. However, if you are unaware of the existence of any unlawful earnings, you are not required to dispose of anything; for the unknown is as if it does not exist.