"scriptSig" for P2SH-P2WPKH
I understand that: in "asm" i have RedeemScript. In txinwitness i have my signature and the pubblic key. Correct?


Correct. in a P2SH-P2WPKH the witness contains the signature and the public key, and the script signature contains the redeem script.


  is it correct to say that, as an additional condition, to unlock a UTXO P2SH-P2WPKH, compared to a P2PKH, you need the HASH of an additional public key?


This is where you are kind of wrong. 

The address of a P2SH-P2WPKH is the hash160 of the serialized redeem script of the P2WPKH, which has to be OP_0 &lt;hash160_of_public_key&gt; according to BIP0141. So it looks like you need an extra public key, but in reality you are just using the same public key twice. One that goes inside a redeem script to the script_signature, and another for the witness field that goes naked alongside the signature. 

In other words, there is no extra public key. It's the same public key that is wrapped inside a smart contract (redeem script) defined by BIP0141, serialized, and then hashed. Now, this hash is the same hash used for the public keys (hash160), therefore the outputs of these smart-contract hashes have the same length of those public-key hashes, and that's why they can be confused with public keys when in reality they are smart contracts. This is done on purpose to make P2SH backward compatible .