What is the proper dose of prednisone for an adult following an acute asthma attack?
There is no one proper dose of a medicine that would apply to every situation, including the one you describe. Each person is different, with different levels of illness, different tolerance to medication, different body types, etc. Doctors take a lot of factors into account when prescribing medication.
If you have an issue with a prescription you received, then the person to discuss it with is your personal physician. Open up the lines of communication and get a discussion going. It's OK to advocate for yourself if you're not satisfied with your treatment plan.
P.S. Here are some links you might find helpful as you learn about your medications and your condition:
Asthma Treatments - How to Manage Asthma (a Doctor Q&A)
The Importance of Follow-Up Doctor's Visits
10 Signs of a Great Asthma Doctor