Regarding the potential sale of Chinese company TikTok to Microsoft, Trump "says he told Microsoft’s Nadella that U.S. should get a cut ‘because we’re making it possible for this deal to happen’". Are there any laws that would enable Trump to make this a condition of the sale? Conversely, are there any laws that would prohibit this?
The law which allows the government to have any say in the question is 50 USC 4564, by which presidents have blocked the sale of US property so that they become under the control of foreign persons. For example, the acquisition of two Chinese companies were ordered to divest themselves from Stayntouch, a US company. The sale of Qualcomm, a US company, to two foreign companies was blocked under that same law. The transactions affected are described in 50 USC 4564(a)(4)(B), all of which involve acquisition of a US business by a foreign person. This is the opposite of the proposal that a foreign company be acquired by a US company (I am setting aside the possibility that the government could threaten MS with antitrust action).
Subsection (d) concerns when and how the president can take action regarding a covered transaction, namely that the president deems that it threatens to impair the national security of the United States, and allowed legal actions (in US district courts) are to implement and enforce this particular law. A kickback does not relate / eliminate a national security threat.
Acquisition of a foreign entity by a US entity is not a covered transaction, and Congress did not authorize taxing a US company for the acquisition of a foreign concern. CFIUS or Trump can order ByteDance to divest from TikTok (foreign companies), because that is authorized by Congress.