We believe our tree was frost/frozen. Should we fertilize/prune & when?

Where do you live? It helps to know the growing zone you are in, folks down south are just starting summer, but folks up north may still have snow.
If this is a Japanese Maple there is a good chance it's the same as dead. Is the tree located in a sheltered area away from direct wind? Doesn't look like it was mulched? Did it leaf out at all this year?

Before you do anything, check to see whether parts could still be alive. Scrape the bark in various spots to determine if it is dry and dead or still green underneath. Also try snapping off a twig, if it just bends, it is not yet dead. Cut off any dead parts; the live part may recover with time

If a Japanese Maple, our condos had several bitten by an ice storm. They looked dead last summer, but some of them have leafed out now this spring. So I would not give up on it yet. Good luck!

I agree that if it is a J. maple they are very resilient. I've taken in several 'scratch-n-dent' J. maples from my cousin and sometimes they take a couple years to recover, but then they go gung-ho. If you don't mind nursing it along you may be surprised.

too. First scrape the bark a tiny bit in a few spots on the branches with your thumbnail to see if there is green under it. If there is, the tree is alive. It doesn't look dead to me.

Then, yes you should begin watering and fertilize it. But before you do that, you really should weed out all that stuff underneath it, in a circle at least a couple of feet wide around the trunk. All those weeds and grass are competing with the little tree for water and nutrients.

After you weed and fertilize, lay down some organic wood chip mulch. It will keep the root zone cooler and more moist and help the tree a lot both through the coming heat of summer but also VERY much help it through winters to come. Just don't pile it up against the trunk, keep it an inch or two away. The mulch layer should be maintained at 3 inches thick or so for good insulation and weed suppression. Add more in fall if you have it, or just pile your dead leaves around the tree, too.

Japanese maples may do well farther south, but I lived in zone 5 and never had any luck with them, and they grew really slow for me. I thought of them as fast growers, maybe the longer growing season of warmer zones helps w that. Around here if they are not in a sheltered area, they tend to die, don't like wind. It may depend on how mature a root system the tree has and such.

They do well in the Pac. Northwest, too. I think it's more related to soil type than climate, they really like acid soil and lots of humus. they don't grow worth a darn in Salt Lake City, either. Alkaline clay and dry heat are not even close to welcoming to them. But in a pot or a raised bed with good soil, mulch and shade they do fine. It's zone 6 there, too.

Frillylilly is spot on. I live in zone 5b and wanted a Japanese maple with red foliage for my back yard. After doing research, i found out that even a Bloodgood would need to be protected in my zone. Especially from the winter winds. Japanese maples with green foliage seem to do better here though. But ultimately i got a "jack frost" maple. Which is a hybrid tree of Japanese and Korean maple.

We chose to plant Sambucus 'Black Lace' in my daughter's garden in Utah. Looks a lot like Japanese Maple, but much less fussy. And it flowers.

Another interesting maple is Variegated Sycamore Maple (Acer pseudoplatanus 'Eskimo Sunset') which is a sycamore maple. Not sure how large it will eventually grow, I've had mine for a few years and it is slower growing and/or shorter than Sycamore Maple (Acer pseudoplatanus 'Spaethii') which I also got about the same time and is now twice as tall/wide as Sunset. Per Monrovia, Sunset will grow to 12' in 10 years, and top out at about 25'.