Questions can be asked. However, where you stand in the JW organization, combined with who you ask the question of, decides the reaction you will get.
For instance, if you are a newer associate and you ask your Bible Study conductor why the blood doctrine has changed over the years, you'll likely be treated kindly and given the most recently printed info, along with the line that the Organization is so progressive and really has God's spirit in looking out for the people.
On the other end of the spectrum, let's say you are a brother who was born-in, a long-timer, in good standing, with elder or ministerial servant credentials. You ask one of your fellow "appointed men" why the Society is so wrong in its understanding and teaching of evolution. Red alert! You should know better! You're supposed to be an example to the congregation! How could you doubt the Society?!
Little children, extremely elderly ones, new members, unbelieving mates, Bible studies, poorly educated people, "spiritually weak" ones and the occasional congregation crackpot are usually allowed by the JWs to ask questions freely. The reason for this is because the JWs are so convinced that their understanding of spiritual things is far more superior than anyone elses. To them, you are just inferior in your thinking, a "spiritual babe" who is not yet ready for "solid food." It's quite condescending and arrogant.
Pioneers, born-ins, elders, servants, their wives, their children , long-timers in good standing and anyone else who the JWs think should know better are not usually free to ask questions that express any hint of doubt. These ones risk either alienating themselves as a threat to the congregation or, being downgraded to one of the lesser ranks (weak, crackpot) mentioned earlier.
This is just my observation. Would anyone like to weigh in on this analysis?