Correct pronunciation ?

Mostly, keep one general rule in mind, but it is only a general rule: Unstressed vowels tend to go toward the ə sound very much when they are spoken in normal speech, especially American speech.  ʌ  is used for the same sound in stressed-vowel syllables, like the 'u' in 'butter'. Next, if you do say something like 'komand' in words that are like that (not all of them), you will still be understood.  ...  Some of the others that you are using as examples above are not very clear examples with the "phonetic" symbols and respellings that you have used.  

There is some humor inspired by your overly cautious question, Ali.  Why?  As a 75-year-old wordsmith and poet, I remind you of how many different language patterns exist in the U.S. nationwide.  For example, in Boston (or as Bostonians often say, "Bahstin") an extra 'h' added to its 'o'; in New Jersey (pronounced Joisey by locals); and my home town of St. Louis in Missouri often becomes "St. Looey" in "Missourah" when pronounced by Americans not native to Missouri.  

The precision you seek for your own use is not very prevalent among the people with whom you will be communicating.  See the humor?  Relax and be yourself.  You'll do fine.  

Vowels are typically pronounced differently in words than when you say the letters by themselves. Learn correct pronunciation.  Also there are so many mistakes in your English that it's difficult to read, and makes me seriously question the quality of the education you received. Either that or you weren't a very good student. The number & nature of the mistakes are very inconsistent with what one would expect of someone who allegedly hold's a Bachelor's Degree in English.

Please do not teach English. You are not qualified in any way.

Nobody cares about the fine detail of those vowel sounds. You will be understood whichever way you pronounce "command" or "derision" or "deposit".

Those particular issues have little bearing on your comprehensibility since they are not meaningful differences in English.  Stressing correct syllables is far more important.

I am a holder of A bachelor's degree in English [language].

I have a question about THE pronunciation of some vowels. As you know better than I DO  ["me" DO??].

Must I pronounce the words containing them [exactly true] correctly?

Judging from your English, you do NOT have a degree in it.

Come on: there are so many different accents and traditions in England alone, let alone elsewhere in the world. What is correct in Cornwall may not be understood in Yorkshire, Texas or Brisbane!

Good dictionaries give the guidance for each word, so look there. I don't know the work, "conmand".