Is it possible to buy a stat of 16? I am pretty sure you can't but wanted to see if I was wrong. I would like to play a Dragonborn Cleric but still have 16 Wis
Only if your DM allows rolling for your stats, and you get lucky. But rolling is a common (some even say default) method, and rolling a 16 isn't that unusual.
There's no way to buy a 16. I suggest you confer with your DM, and see if he might make an exception for you. You could potentially trade your +1 Cha for +1 Wis. Maybe you come from a less charming but wiser draconic lineage. 
As said before, you can't using point buy. Having 16s available would allow some races to start with 18s in primary ability, which actually limits options. As it is, having a +1 from you race is enough to get you just a high as a +2 from your race in terms of modiers. Using a race with only a +1 in your primary abiliy would become a less attractive, and thus unused option.
But you don't need it. 15 is high enough to be effective, particularly for a cleric. Many of your attacks can be weapon based, and your Dragonborn Strength bonus can easily start that at 16. Support spells (a cleric's bread and butter) generally don't require attack rolls or saves, so a high Wisdom isn't necessary to use them effectively.
This edition seems to be much more forgiving of making less than perfectly optimal PCs, especially with the capped stats. If you want a Dragonborn cleric, I'm sure you can make it work and will be happier for having made the less obvious choice.