You see? This is why I dislike the use of the terms objective and subjective. Everyone says they understand what they mean. Everyone has a vague idea. But they truely don't have much in the way of definition.
A question you should be asking is, 'If something exists that I can never observe or measure, will I be able to define it?'
This type of thing is an example of how philosophers can take a very simple concept and break it down into incredibly complex servings.
But...here I go anyway -takes a deep breath-
Is there an objective reality which exists independent of subject reality?
Term confusion. Scroll down to the end for more thoughts on this.
Is existence real?
Define your terms. If existance is based solely on an ability to measure and define an objective 'verse. No. If existance has a more micro definition, localized solely in a human's perceptions, then yes.
Objective reality may exist, but only the "community construct" "sujective reality" is meaning because objective reality is entirely unknowable?
Philosophers point to interlocking 'realities' in order to point to a reality not limited to one person. (I'm presuming this is what you mean by objective and subjective) Cause and effect. I kill a person. That person's existance ends. Therefore I can affect a broader reality.
Is existence an objective reality?
So here we are, defining this term existance. Really, we should do this before asking any other questions about it. Is 'existance' the interlocking reality or the inner reality. I would lean to something broader, encompasing both. Existence seems to lend itself to a definition based on cause and effect. Is one's existance over merely after they die? Or do they continue to exist until their influence has left the stream of the world? Does Adolf Hitler 'exist' in today's world?
Does the unknown exist? (That is can an object/phenomenon be said to be real if it has never been observed or measured?)
Using this definition of existance we just hashed out above, the question becomes, does the unknown have influence on the world? Something unobserved and unmeasurable... This is the god question. Other people have written volumes...
Can I be certain of the existence and reality of anything other than myself?
Using the definition of existance, does anything other than you have an influence on your life? ... I would say so. Therefore something out there must exist. Ha! Love the logic!
Does observing an object or phenomenon changing the objective reality (nature) of that object or phenomenon?
What the hell was the name of that theory? Any isolated biosphere, when studied, changes. It seems reasonable that identifying any currently unidentifiable thing would change the way it affects the people who identified it.
Does anything exist that I can never observe or measure?
Does anything that you cant observe or measure effer effect you? Sometimes, the key to answering a philosophy question is to turn it around onto yourself.
Is objective reality mutable, that is, can simply observing an objective reality (eg a fact) alter that fact?
Term confusion. Localized around the word Objective. To be objective is not to be fact. To be objective is to be independent of all other influence. This does not exist in reality. In fact, as one of the traits of reality is change, objectivity seems to be the anthesis of reality.