The first regards the ownership of the company which hired Joe Biden's son Hunter for an exorbitant amount of money while Joe Biden ran the US Ukraine policy.
The second question is about the firing of the Viktor Shokin, the former Prosecutor General of the Ukraine. Trump accuses Joe Biden of having intervened in favor of his son's sponsor to get Shokin fired. The timeline below supports that assertion.
At Naked Capitalism Yves Smith reposted a 2014 piece by Richard Smith who at that time looked into the Hunter Biden appointment to the board of Burisma, a Ukrainian gas producer. Yves writes:
Richard [Smith] did a deep dive into the dodgy appointment of Hunter Biden and then Secretary of State John Kerry's long-standing bundler, Devon Archer, to the board of Burisma Holdings. Richard quickly got past the noteworthy fact that Biden Jr. was being paid quite a lot for no relevant expertise and no investment in the company…so what was he being paid for, exactly? Oh, and Richard also describes how Hunter's and his uncle James Biden's past financial rides were with con artists.