Where do I find my titanium card number?

You don’t. You can find your card details in the Wallet App on your iPhone. Wallet->Apple Card->touch the small credit card icon at the top right, next to the search icon (magnifying glass) and your card number with other card details will display.

But this may not be the actual Titanium card number. However it can be used for online purchases and such.

Remember, the Apple Card is not a traditional credit card and was designed from the ground up with the utmost security in mind.