First off, I’m assuming the board has no significant damage other than the normal bumps and bruises that can be sanded out.
The first thing you need to do, again I assuming the finish is pretty much gone, is sand the whole dagger down to or close to raw wood. At least get it where it is nice a slick. Any varnish that is there and still tight is fine to leave behind.
Now for the finish. I have used Cabot in the past. It is more readily available for everyone and not as costly as Interlux and other true marine products. You do get what you pay for here but on a dagger that won’t live in the water and shouldn’t really have that much uv exposure the Cabot should work fine.
If you are down to or close to raw wood then your first coat should be a well thinned coat of varnish. I would thin it close to 45%. What you are trying to do is really penetrate and seal up the wood. You may even want to put a second coat like this after you sand the first coat. I would especially consider this if the first one raised a lot of grain and you had to do much sanding. On the remaining coats I would thin the minimum you can to be able to put the varnish on without it pulling. You may be able to go with it full strength but you probably should consider thinning it 5% of 10% with thinner. If you are careful to always keep a wet tip on your brush you will get better full coverage with thicker varnish. I think your best bet is to put 5 or 6 good coats on the board. Cabot does have less solids than the higher priced varnishes. I know on my site you see that I only put 3 coats on. I do this because of the various ways people use the products. Some are kept in the garage and rarely used while others are kept outside in the sun and used all the time so I let customers decide if they want more.
I hope this helps you Chester. Let me know if you need more info.