Answer:
Similarities:
- Both places are to worship god
- Anyone is welcome
- People pray to get closer to god
- Decorated internals
Differences:
- A Gurdwara has a "Langar" hall when anyone can eat if the want to and they can practise "sewa" which is that act of helping the Gurdwara keep clean whereas mosques do not
- In a Gurdwara your head must be covered preferably by a turban if you abide by the 5 K's but a holy cloth would do whereas in a mosque you don't need to cover your head
- After you have prayed in a Gurdwara you can receive a holy blessing of food called "prashad" which a sweet type of soft texture flour based sweet. This is optional but highly recommended. In a mosque you don't receive any physical sweet after praying.
- Sikhs worship a book called the Guru Granth Sahib which is the holy book of Sikhism. It gets taken care of just like a human guru. Anyone from any caste is welcome into a Gurdwara.
- The first things Sikh's do when praying is touch their forehead on the ground which shows respect.