First question:
"Which one is the thicker?,dictionary or comic book."
>> "Which one is thicker? the dictionary or the comic book?
The answer is,
"The dictionary is thicker than the comic book.
* Don't forget the use of article THE.

Second question:
"How much the lion weigh?"
>> "How heavy does the lion weigh?"
The answer is,
"The lion weigh is 100kg."
>> "The lion weighs 100kg." / The lion's weight is 100kg. (Weigh is a verb while weight is a noun)
* HOW MUCH is used for amount or price / degree.
Examples:
- How much is your bag? It is 17,000 won.
- How much do you love your parents? I love them more than myself.

Third question:
"How long the elephnt?"
>> "How long is the elephant?"
* Be careful with your spelling of elephant.
* Don't forget the use of be verb IS.

The answer is,
" The elephant is 5meters long.
>> " The elephant is 5 meters long

Thank you for doing your homework, Andrew! Two thumbs up!  Have a terrific Tuesday!