To put it another way... your "wallet", is essentially like a safe that contains a keyring that has a bunch of safety deposit box keys on it.

Meanwhile the bitcoins are stored in various safety deposit boxes at a secure facility (aka "The Blockchain"™)...

So, to figure out how many Bitcoins you can actually control, you'd need to open up your safe, take out all the keys and then open every box that you have a key for. You can't simply look inside the safe and see a pile of "X.XX Bitcoins".

As Danny explained, this is what wallet software does... it tracks all the transactions being made on the blockchain, finds the ones that are related to the keys it controls and updates it's balance accordingly.

So, the "Wallet Inspector" you are looking for, is the software that created your wallet file... in this instance, Bitcoin Core (specifically, version 0.18.1 as indicated in your other thread)

For Bitcoin Core, you need to start the application, let it sync the blockchain (likely to take a couple of days)... and then once it is finished, it will be able to tell you what your "balance" is.

If you don't want to (or can not) sync the blockchain due to time/diskspace limitations... then you will need to find yourself a different wallet application that does not require a full blockchain download, and then you'll need to transfer your private keys to that.

Perhaps use the "helper" here to find a wallet that meets your specific requirements: https://bitcoin.org/en/choose-your-wallet