Technically, you would not (or should not, from the point of view of the LSAC) be able to tell which section is the experimental. What you would be able to tell for sure is which area of the test your experimental section lies: for example, if you end up having two section of logic games, then, obviously, one of them is experimental. But, I assume that you are more interested in knowing whether you can tell which section, specifically, is the experimental. Here are some clues, gathered from my experience, based on which you could *potentially* tell the experimental section:
1) Look at the number of questions. Typically, we know that a reading comprehension section is made of 27 questions. So, if you get a reading comprehension and it is composed of a much smaller amount of questions, say 22, then it is *likely* that it is experimental. We also know that a logic game/analytical reasoning section is typically composed of 22 questions, and logical reasoning 25/26 questions.
2) Look at the nature of questions. We know the typical question types of each area of the test. For example, for reading comprehension, you definitely will get a main-idea question type for every passage. We also know the nature of passages -- typically, you will for sure see a passage that presents arguments of both sides of an issue, a passage that presents the author's own view on an issue, etc. If you see a section of reading comprehension that is composed of passages that fall out of the ordinary range of topics/structures, then it is *possible* that it is the experimental one.
3) Feel the difficulty. It is true that one's own judgement of a test's difficulty level is likely affected by a variety of factors (some of which are dependent on the test day conditions), and this judgment also likely differs from another person's judgement. However, the more practice tests you do, the more likely you are able to see that the difficulty (subjectively measured, even) of tests fluctuates within a *very* small range. If, say, you are generally pretty good at logic games and that, for the last 10 practice sections of logic games you've done, your "feel" of difficulty level of games is a certain way, then, it is unlikely that, on the real test, a real logic game section would completely throw you off and feels extremely difficult to you. When you have a lot of experiences/practice to go with, your judgement of whether a section is an experimental section is more likely to be right, compared to a person who does not have a lot of practice tests under her/his belt.
At last, I just want to say that one should not worry too much over the experimental section. Truth is, so long as you put in diligent effort and practice and have done and reviewed many full-length practice tests (10 minimum, in my opinion) prior to your test, you will very likely score within the average-to-above of your practice tests score range.
There is no secretes to the LSAT; this test is absolutely learnable and improvable, for those who are willing to put in the work.
