It’ll be a jin, but reduced significantly in size. I’ll decide by how much it will be reduced during styling, but I think it will be significantly smaller. It’s just kind of boring - straight and no taper.
In terms of a tutorial, I think that Bjorn has a pretty good one on BonsaiU. I’ll give you the basics. First, identify the areas that are clearly alive and the areas that are clearly dead. In this case the area just below the straight trunk is clearly dead. Sometimes, especially with old, collected trees, the live vein will have swelled beneath the bark relative to the dead wood and that can help. I use a small gouge and slowly work from the deadwood to the live vein and I remove a small piece of bark. When you get to the live vein, you’ll notice a distinct color difference - under the deadwood the exposed sapwood will be a light yellowish brown color. Under the live vein, the sapwood will be much lighter in color - almost white. Sometimes you’ll see a little pink as well. Now you know where the live vein is at one point. Repeat several times until you have identified the trace of the live vein under the bark. Then I mark it with a permanent marker and use a sharp knife to cut through the bark all along the edge of the vein. Then I have a set of different shaped Jin tools that I use to scrape the bark all along the line. You can use increasingly aggressive tools the further you get away from the live vein. I use a bark stripper once I have things down. Just remember - every bit of foliage is connected to a vein or veins on the trunk. Trees commonly have more than one live vein. So before you just start in with the bark scraper, make sure your positive that you know exactly where the live vein is and that you have found them all.
S