Notice from information and criminal investigation

I just received (almost an year later) for taxes which I had filed last year for the FY 2013-14.   It says that PAN number not furnished for certain transactions.  They have asked me for PAN card and ITRv acknowledgement.    I just sent them the information.

When I recalled what I did in 2013-2014 - there were 2 mutual funds sale which I forgot to declary in my taxes and also there were a lot of international credit card transactions which I did.    So, I am not sure which one is causing the issue.

If it is mutual fund - what documents do I need to be prepared with ? and what is the possible penalty/interest ?

Thanks,