Does multiculturalism challenge notions of national identity and citizenship?
Define multiculturalism ? this is different in different countries so indicate you are aware of this (it is a political ideology).
The theoretical literature discusses the numerous variations in multiculturalism from weak through to radical multiculturalism (so, some may be a threat and others may not ? you need to indicate you know there are multiple versions).
Establish/discuss how national identity is formed and the role citizenship may play in this.
Consider using particular case studies from particular nations to argue your case.