What is the easiest way to add the right amount of fertilizer to finished compost to make it suitable to grow tomatoes?

The Easiest way would be to simply use the Compost as the Fertilizer. If it is good compost it will be nutritious enough to yield good fruit. You may wish to spread a thin layer of mulch on top of the finished compost.

Right now I am preparing my soil for Tomatilloes to grow. I buried the entire Tomatilloe about 10 inches deep. On the surface are rotting tomatoes. I plan to pour Salt Water from the Ocean over the dissolving tomatoes which will drain down and surround the fruit.

(Note that I use experimental methods.)

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The easiest way (unless you are a soil scientist or specialist) is to combine your finished compost with your soil & then send in a 1 lb sample to the agricultural extension office in your area to have it professionally tested. On the form, indicate the type of tomatoes that you will be planting and they will recommend the optimal nutrients to add to the soil. Since some tomato varieties require quite a bit of nitrogen & some soils are low in nitrogen, adding only finished compost to your soil will NOT be sufficient to grow a crop that will have a high quality yield.

And whatever you do, do NOT add sea (salt) water to your soil (as describe above). Too much sodium will cause serious problems for future growing.

Note: typical additions of compost to soil are usually done by adding 1 to 2 inches of finished compost to the soil & then mixing it into the soil thoroughly.