Is Sudan democratic or republican?

The terms democratic and republican are NOT opposites. It is possible to have a democratic government as a republic or as a monarchy.

This means that your question can not be answered.

Sudan titles itself as "Republic of the Sudan", a Federal presidential, constitutional republic.

However, Sudan is known to be one of the most corrupt nations on Earth and while this state persists whatever Sudan titles itself is meaningless - there is no effective government of any form, the country is anarchic and riddled with Muslim extremism.

The ordinary people of Sudan need to take charge of their country in order to solve their problems and join the civilised countries of the world.