Is it possible to read a text file inside a password-protected zip file without the password?
No. There are two ways of zip encryption, a classic one, which is weaker, and a newer one based on AES.
In both cases the password is needed in order to decrypt the contents (i.e. it's not just UI, where you could be asked for a password without the program actually requiring it to read the file). So the process would involve breaking the password (which would be more or less complex depending on the algorithm used and how the password was used).
At most, you would be able to obtain without decrypting, in addition to the filename, the CRC32 of the plain file. But although that would help if you already suspected what the content was, it probably won't be helpful here, even if it is just a line of text.
No, nowadays zip files are protected by AES. This will hide all of the plaintext in a way that you can only recover it when you have the key. The only other thing you can see is the size of the plaintext as that is as good as identical to the size of the ciphertext.
Hexadecimals are just a readable representation of the bytes that make up the ciphertext. However, as the ciphertext will consist of byte values indistinguishable from random, that will not help you one iota.
Unfortunately, not really.
What you must understand here is that we are not speaking of a file that "is there", access to the original contents is not actively being blocked by the zip software you are using. That would make password protection essentially useless, as another software could just show the file without asking for the password, right?
Instead, the file content itself is cryptographically encrypted, and the password you are being asked for is the actual decryption key itself, which is required to transform the encrypted contents to their original form.
In theory, it is possible to brute-force the key, but this is only possible in practice if you have a finite (and "not too long") list of possible keys, or if the key is considerably short (which, according to your question, does not seem to be the case).