Parting tool.
Push it straight across as a scraper to start the cut; just a quick start to get it going. That initial scrape will prevent the parting tool from feathering the inside edge. Pull the parting tool back, tip it up, and bevel cut the remainder of the tenon. (Don't scrape the entire tenon, or you will put a lot of wear and heat on your parting tool.) Gently push the bevel forward
and down as the tenon is cut. You will see and feel the action as you make the cut. Any non-woodturner who watches you will think you're a pro.
Confession Time:
There is a certain raw pleasure in making tenons on a lathe with a parting tool. It is fun to watch the wood go down as you cut the tenon. Fun, as in two-year-old knocking down a tower of blocks fun. Try not to jump up and down and squeal with delight in front of others as you make tenons.
This is my parting tool; it came as part of a six-piece turning tool set:
https://www.robert-sorby.co.uk/b830031-standard-parting-tool
(Mine is the 1/8 inch version with a handle, third down on the list.)
Parting tools come in many shapes and sizes. One of my experienced woodturning friends needed a parting tool for the shop a few days ago, and he was very pleased with this one:
https://www.robert-sorby.co.uk/b830s08-slim-parting-tool
You didn't say
why you want to make tenons. If it is for pen turning, then you're done. Measure carefully. It is easy to cut off, much harder to cut on.
Some people make dovetail tenons for mounting bowl blanks in a chuck for hollowing. Dovetail tenons have a slight angle to them to match the angles in the chuck jaw, making a better grip. Nova makes a special dovetail turning tool with just the correct angle to match their chucks (and probably most other brands of chuck). I do not have one. Instead, I use a diamond carbide tool to shape the angle after cutting the initial tenon. It doesn't have to be the exact perfect angle as long as the chuck has firm grip on the bowl. I like the diamond tool because it is more versatile. It has many uses, such as making decorative "grip" lines on pens.
Nova dovetail turning tool that I do not own, at least not yet:
https://www.teknatool.com/product/nova-dovetail-chisel-chuck-accessory/
Diamond carbide tool that I use, it works well enough for me and has many other uses in woodturning:
https://www.rockler.com/full-size-diamond-ergonomic-carbide-turning-tool