How to access the Character Stats

There are multiple ways to do it.

Basically I presume you know where in the DefaultCharacterSelectionScreen.cs file it gets the highlighted character?

CharacterInfo character = this.selectableCharacters[characterIndex];

From there you'd just get or set the properties as you see fit.
For example, if you want to show their blood type in a text box on the gui, start by adding a new public instance field that you can drag and drop the UI element from the hierarchy to. Then in the code you'll just reference that item.

public Text bloodTypePlayer1;
public Text bloodTypePlayer2;

Then, in the code after you get the character, in the if check for each player you'd just add a line to populate that object's text value with the character's blood type. Something like this:

 if (this.bloodTypePlayer1 != null) {
this.bloodTypePlayer1 = character.bloodType;
}

Did you do the UI work to add the text element for which you want to populate with the blood type?

You would open the character select screen from the global options, create the player1 and player2 text boxes in the canvas hierarchy, then click and drag those into the screen's inspector which should have the "Blood Type Player 1" and "Blood Type Player 2" values currently marked as none.

From there, it's a matter of setting up the font type and color in each text area to make sure you can see the text value when running the game. Any values you save in the screen editor won't be displayed when running the game unless it's not updating the text box.

I'll try reproducing my suggestion to verify i gave you the right tutorial later today and will let you know.

Can you show me a screenshot of your hierarchy when editing the screen in Unity?