Here's how I found one of mine when in the Coinbase app: from the homepage click Bitcoin (under "watchlist"). When the Bitcoin page comes up, scroll partway down past the Bitcoin price info to where it shows your balance, then click where it says "Bitcoin primary balance". That'll take you to another page, scroll down, and you'll see your transaction history. Click on the sent transaction that you want to view. When that page appears, at the bottom you should have an option to "view on block explorer", so click on that. You'll get a Summary page and a few lines down will be one that says "Hash", and the beginning of the ID - should have a little icon on the right hand side that will copy it to your clipboard and can then paste into a message if need be. HTH!