I'm from Tajikistan traveling to the US with US tourist visa and transiting through Zurich. I will have cash between $9K-$10K on me while traveling to the US. US border protection has a rule to declare cash above $10K but I'm not sure how are the rules while transiting the Zurich airport. I've tried looking this up on various websites like the following but couldn't find the answer to my question. Note! I'm planning to have the cash in hand not in the checked bag. Thank you in advance. Transferring at Zurich Airport Baggage regulations
This page, from the Swiss Customs authorities, says that currency does not need to be declared, but that there are checks if you have more than CHF 10,000:
Unrestricted amounts of liquid funds, i.e. cash, foreign currency and securities (shares, bonds and cheques) can be imported into Switzerland, brought through Switzerland in transit or exported from Switzerland. Furthermore, the funds do not need to be declared.
Checks on the cross-border movement of liquid funds
To combat money laundering and terrorist financing, we can carry out checks. If you are carrying CHF 10,000 or more, we will question you. In doing so, you will have to answer questions concerning you and the origin and intended purpose of the money, and provide information on the beneficial owner.
Consequences of the checks
In the case of liquid funds of CHF 10,000 or more, an entry will be made in the information system of the Customs Administration. If there is a suspicion of money laundering or terrorist financing, the funds may be temporarily confiscated or handed over to the police. The right is reserved to take other measures linked to combating crime.
Legal situation in the European Union
Liquid funds of EUR 10,000 or more must be declared in writing to the respective customs authorities when entering, passing through and leaving the European Union and its member states.
Given the importance of doing this right and the danger of having your currency seized, by Switzerland or the US authorities, I would encourage you to seek legal advice instead of relying on strangers on the internet, or better yet, simply not do this at all. In the case of the US, traveling with slightly less than $10K could be risky, because the authorities might believe you are intentionally carrying just under the amount that must be declared to evade the reporting requirement, which makes you look quite suspicious.
I recognize that Tajikistan has currency controls that may pose an obstacle, but bank transfers are usually a better option for lawful transactions, due to the greatly reduced risk of loss, theft, or official seizure.