Obama knew of and approved Hunter's Burisma Holdings position:

The Obama administration knew about Hunter Biden’s position on the Burisma Board. Hunter landed the lucrative position two months after he was kicked out of the US Navy for drug use.

In fact the Obama Administration was confronted about Hunter Biden’s position on the Ukrainian Burisma Board in 2014.

State Department spokesperson Jen Psaki was asked about Hunter Biden’s appointment to the board during a press conference. Hunter Biden had no experience in gas or oil and did not speak Ukrainian. He was paid from $50,000 to $150,000 a month for sitting on the board.

JEN PSAKI RESPONSE TO QUESTIONS:
Reporter: Does this building diplomatically have any concerns about potential perceptions about conflict of interest or cronyism which is what you often accused the Russians of doing?

Jen Psaki: “Um, no he’s a private citizen.”

Reporter: OK, then so you consider the Russian oligarchs who control, or the Ukranian oligarchs who control this, they’re all private citizens as well?

Jen Psaki: They certainly, I wouldn’t put them in the same category.