Want to put outside lights on each side of the garage wall. I do not think I have the skill to remove brick to mortar in a box so I was wondering if I could mount the light mount to a nipple fixed to a box mounted inside the garage. Would this be possible and still be within code ?

Depends on where you live, codes vary from place to place. It helps if the garage is not attached to the home. Many outside sconces do not require a box and can be mounted on a block of treated wood which is attached to the bricks with Tapcon screws. Try not to let this happen to you https://www.youtube.com/watch?v=luREkA6zMX4

if I could mount the light mount to a nipple fixed to a box mounted inside the garage.
Not sure what you mean but probably not. Also sounds like a lot of unnecessary work.

Brick is very soft.
Choose your box compatible with the mounting holes of the fixture. I would probably use a round, plastic, ceiling light box.

Choose your location, mark the outline of the box. Using a small masonry bit, drill a series of holes around the perimeter. You can use a regular masonry bit, you don't even need a percussion bit. A good cordless drill should do the job. After you have drilled the perimeter use a piece of 1/2" black pipe about 8 to 10" long and a heavy hammer to knock out the center. You could also use a cold chisel and hammer.

I am guessing that you have a brick veneer wall (one brick thick) not a true masonry wall (brick and block). After opening up the brick for the box, drill through the sheathing for your cable. Install your box screwing it to the sheathing. If you really want to be neat, seal between the box and the brick with Liquid Nails.
Note; If you use the box shown, the hole for the cable will be off set, not in the center. There are other round boxes that have wiring hole in the center of the back.

If you have a true masonry wall (brick and block), punch through the block with the 1/2" pipe. "Glue" the box in place with Liquid Nails.

Do your wiring.

Why not an outside wall mounted pancake box? Only 1" thick. Mount it with Tapcon and run cable through the brick using UF wire.

Brian
I'll go along with the pancake box but why the UF cable?

Brian
I'll go along with the pancake box but why the UF cable?

That sounds like something an inexperienced inspector would ask for... or some mis-guided local code interpretation of a "damp" area.