I'm going to go through this step by step.
First, start by opening the weapon you would like to a Sneak Attack Query to (in my case, it was all of them). To do this, hover over the the weapon name under Attacks & Spell Casting. This will cause a cog to appear. Click on this cog.

Find the Damage 1 field. Here is where we will add the query for Sneak Attack.

Using the current weapon damage value add the following.
+ ?{Sneak Attack|No, 0|Yes, [[ ceil((@{base_level}) / 2) ]]d6}[Sneak Attack]
So in the case of a Rapier that does 1d8 damage, the text entered into this field would be
1d8 + + ?{Sneak Attack|No, 0|Yes, [[ ceil((@{base_level}) / 2) ]]d6}[Sneak Attack]
The posts above talk about type for something else I was trying to do. They have nothing to do with adding the damage value. Just change the damage value in this case.

Finally, depending on how your damage is output, either automatically or not, you may have to choose when to query the attack. Personally, I have mine set to don't auto roll damage (because I would hate to see what could have been).

When I click the Rapier attack now, it just shows the attack roll. I need to click the name of the attack to actually get the query for Sneak Attack (Sneak Attack is additional damage that is made when you HIT, so this works well here).

Once I click the name of the attack, I will be asked to choose if it was a Sneak Attack.

Once I choose yes, you can see that the damage output now includes this value.

If instead you choose the option to auto roll damage above. The process is similar, except, as soon as you click your Rapier Attack you are asked if it's a Sneak Attack without knowing if it was a hit or not. This will automatically output to chat with the attack roll and damage.

And finally, in both cases, you can choose no when asked if it was a Sneak Attack and it will roll damage as normal.
