After spending hours and hours of researching on different aspects of philosophy, not to mention the effort, here is my question:
What is the point of acquiring knowledge when time would take it away soon enough?
What's the point of working when all money will eventually perish?
Why bother going to school when your brain is just a temporary storing unit that decays and will eventually perish too?
Why do anything, knowing that nothing will be worth while and that eventually everything will be destroyed in the inevitable heatdeath of our universe?
Thing is, you're right. What you're staring into is called Nihilism, but there are many forms of it. You could also look at the same theory, only from a more positive perspective:
Why worry about the results of your final exam when the results will be forgotten in only a few decades?
Why feel bad about what you said at some point to someone when both you and the person will die in the end, leaving no negative relation behind?
You see, this is a huge topic to discuss. Nihilism though wouldn't be the first thing do delve into if you're just starting to read books on philosophy. There are no right or wrong opinions about Nihilism as far as I can tell, the only lesson I'd take from it is that - everything will be gone at some point. You, this world, this universe, nothing is meant to be eternal. This, I think, gives every moment, every day and every small thing you do, taste, see, hear, an inherent value, because eventually, you won't be able to experience any of this. Cherishing the moment and accepting that - although it sounds scary - everything will die at some point, gives you a kind of freedom that can be quite the opposite of the feeling you'd get from reading Nietzsche or thinking about Nihilism as this dark, scary, brutal thing.
If you're interested in this topic, I'd recommend you'd buy some books on it. Nihilism is one of the most well known philosophies because of its edgy image, so it probably won't be hard to find literature on it.
This isn't necessarily about death or the end of the universe (as other answers suggest). You may as well ask: What's the point of eating ice cream if the taste goes away shortly after? What's the point of going on a trip if it's going to end anyway? You could ask those questions even if we and the universe continued to exist forever.
You seem to be suggesting that for something to have any value it has to continue forever, or to have eternal implications. But why should you think this? For one thing, why think that less time means less value? For another, even if less time does mean less value, why think that finite time means no value at all rather than just less value?
One way to challenge your eternity requirement would be to say that pleasure is one thing that has value even if it's finite. Obtaining knowledge is just another pleasurable activity, although of a different sort than eating ice cream or listening to music. Less time might mean less value on such a view but finite activities could still have value and be worthwhile.
Here's another argument that I like that challenges your assumption. Thomas Nagel, in his 1970 paper "The Absurd", writes:
It is often remarked that nothing we do now will matter in a million years. But if that is true, then by the same token, nothing that will be the case in a million years matters now. In particular, it does not matter now that in a million years nothing we do now will matter.
Later in the paper he concludes:
If sub specie aeternitatis [=from the perspective of eternity] there is no reason to believe that anything matters, then that doesn't matter either.
So, if you think that nothing (or some specific thing such as acquiring knowledge) matters eventually, the same reasoning should lead you to think that it doesn't matter that it doesn't matter. And if it doesn't matter, you shouldn't worry about it.
Speaking within the domain of our perception (that means, accepting that things exist, that causality is something natural, that we have goals, etc.), and excluding any physicalist perspective (that is, excluding physics, quantum mechanics, the inexistence of causality and goals and so on...), our ultimate goal (as human beings, not as rational individuals) is to survive. Since we tend to act as coherent entities, our rational goals tend to be aligned with our bodily goals. So, in final terms, we can conclude that we want to survive.
In order to survive, we need to interact with our environment and the systems that dominate our perception (things, people, animals, plants ideas, etc.). For that, we need to know all of that. So, even if we are going to die, our curiosity will be with us until our final instants. It is natural for us to search for knowledge, in any conditions.
In fact, that's why you are asking this question.
Empirically we can predict that we will all die and when that occurs time will take away the knowledge we have acquired. We can see that this loss of knowledge could occur even prior to death with diseases such as dementia and Alzheimer's.
There are philosophers who claim that there is an eternal reality underlying this temporal flux. Dominic J. O'Meara describes the "two worlds" of Platonism and Neo-Platonism as such (page 12):
The material world exists only to the extent that it shares in the eternal being of the Forms, just as a shadow exists only as the shadow of something.
Knowledge would then be a way to leave the shadows and participate in these eternal Forms because our Souls are eternal as well.
Even if one accepts that, other questions arise about relationships between the shadow world and the eternal world, such as: Is there reincarnation? If not, what happens to the eternal Soul?
Regardless of these other questions, what such alternatives provide are rational ways out of the problem offered in the OP's question. That is, there just may be a point to all of it.
One way to explore that is by making hypotheses. Assume there is a point, and perhaps make other assumptions along the way, and see where that leads.
O'Meara, D. J. (1995). Plotinus: an introduction to the Enneads. Oxford University Press on Demand.