There's very little out there- I only found a fact sheet: Ethnologue report for language code:nde
Use the student as a resource- can you identify any persistent features of the English that could be L1 interference? Try to make a list of things they do repeatedly, then run up a questionnaire about their language and see what comes out. For instance, if they confuse singular and plural or don't use the plural much, it could be that their language has no plural, so formulate a question around that. Depending on their knowledge of metalanguage, you could simply ask them things like whether their language has tenses, though it might be better to try to get them to translate a couple of verbs in different forms and see.
BTW What level is the student?