The missable commendations are:
Lost Memories
Strike Yer Colours
Forgotten Memories
Treasure for Eternity
Key to Freedom
I have included a brief text description, but if you want the full descriptions with pictures, then I suggest using the excellent guide links provided. I like these guides because they aren't full walkthroughs, so you can still experience the Tall Tale.
Lost Memories:Full link - https://rarethief.com/captains-of-the-damned-tall-tale-journ...The first three journals are in the Bayou part, and the last two are in the Fort. Make sure to pick up the Flame of Souls (story-related) before looking for these journals.
1. Damned Journal 1 - In a row boat found near the blocked green gate that your ship can't go through, turn North. Row a bit until you see a hut on your left. Jump out to it and light the torch for the journal to appear.
2. Damned Journal 2 - Row straight East until you see a mast leaning against a rock. Get out of the rowboat next to the big rock and follow a small river Northeast until you find another hut. Light the torch and this time it will make a torch path. Follow it all the way back to the water. Dive down for a swim to find a sunken row boat the journal.
3. Damned Journal 3 - Get back in the rowboat and row Northeast. Look for two cages hanging from a mast between two rocks. Get to the bottom of the mast on the rock and light the torch. You can now shoot the rope holding the cage with the journal in it.
4. Damned Journal 4 - At the Fort, light the four lanterns around the well in the courtyard. Jump in the well and find the skeleton with the brazier to light for the journal to appear next to him.
5. Damned Journal 5 - After you get back to the courtyard, light the lantern in front of the jail cell next to the well. The journal will appear next to the skeleton but you have to get it from jumping from up top. Do the story-related stuff to start the climb to get to the top of the Fort. Navigate to the top of the jail roof and jump in to get the journal.
Strike Yer Colours:Full link - https://rarethief.com/how-to-do-the-strike-yer-colours-comme...After all the Fort stuff is done, you will sail to the town of Isla Tesoro. The first thing to do when you get here is climb the walls and shoot a cannon at the uninvited guest.
Forgotten Memories & Treasure for Eternity:Full links - https://rarethief.com/captains-of-the-damned-tall-tale-journ...
https://rarethief.com/how-to-do-the-treasure-for-eternity-co...1. Journal 1 - Entering the town, there are some townspeople gathered around a well. Snag the Mercado key off the well for the 'Treasure for Eternity' commendation. Now travel to the clothing shop right after the people and look left on a stool for the journal.
2. Journal 2 - Continue following the path and eventually down some stairs, there will be a barrel with 'xxx' on it on a left turn. The second journal is on a crate shortly after turning left in the tunnel path with the barrel.
3. Use the Mercado key - There will be an auction happening across the bridge in front of a big store that says 'Mercado'. On the right side of this building, there is a door for your key. Light the torch in the room.
4. Journal 3 - Walk past the auction to a small dock and enter the rowboat with some skellies in it. Row through the canal and follow a ghost rowboat. Get out of the boat briefly to a dock on the left where the ghosts are shooting at each other. The journal is on a barrel.
5. Dig up the treasure - Return to the rowboat and continue following the ghost boat. They will eventually get out and start digging. Start digging there as well and return what you dig up to your skelly friends in the rowboat for the 'Treasure of Eternity' commendation.
6. Journal 4 - When Jack Sparrow is running through a massive gate, wait to follow him but instead go up some stairs up to the top of the town walls. Walk towards the two ghosts on the wall and pick up the journal behind them.
7. Journal 5 - When a certain build structure falls pretty dramatically, you'll be trying to get down from some rooftops back into the city. Before you jump all the way down though, jump onto a balcony just one level below and pick up the last journal on the ledge of the balcony.
Key to Freedom:Full link - https://rarethief.com/how-to-do-the-key-to-freedom-commendat...This one..should be a bit obvious. You'll get a key to progress moving through the Tall Tale, but there were some fellows in a jail cell that were working hard to try and get that key before you. You should help them out first before moving on.