How to know key frequency prius 2017?

The keys came with a tiny metal tag that has a number on it. This is the number you need to get a new fob that works for the car.

 

It looks like the little metal tag in this attached file. It should have a number stamped into it.

 

I put mine with the packet I got from the dealership that i keep in my file drawer of documents that I might need one day (and never seem to need).

So long as you still have the other key I don't think the little tag is necessary. When I needed to buy a replacement fob for my 2013 Prius I just made sure I got the right sort of fob and had a mobile locksmith come out and program it to my car. He was able to do all that with just the existing fob.

If you lost both fobs then a trip to the Stealership may be your only option.

 

The key number on the key number plate—Toyota’s term for the metal tag, shown in the Owner’s Manual (PDF) as item ③ under “The keys,” page 160—is used only when cutting a new mechanical key for the lock cylinder in the driver’s door. The key number has no role in registering new electronic keys, which is done using a Toyota Techstream diagnostic system, as described in my September 2018 and October 2019 postings. As @MalachyNG kindly mentioned above, this is easier if you have at least one electronic key that’s already working.

For cars built for the U.S. market, catalog Figure 67-12, Lock Cylinder Set, lists the required parts to add a complete key: an electrical key transmitter sub-assembly, 89904-47530, and either a blank mechanical key, 69515-06050, or a pre-cut mechanical key, 69515-06040. (The -47580 part is only for cars built for sale in Korea.)

The radio frequencies used by the system aren’t especially relevant: the fact that two Toyota models might use electronic keys that transmit on the same frequency doesn’t imply that their keys are interchangeable. That said, if you need the information—for example, to determine compliance with your country’s radio laws—you can search the FCC’s equipment authorization database using the FCC IDs given in the Owner’s Manual, pages 90 and 181: NI4TMIMB-3, HYQ23AAB, HYQ14FBC, and NI4TMLF15-1. According to the test reports in the database, the car transmits at 134.2 kHz, and the electronic keys transmit at 312.10 MHz and 314.35 MHz.