He has a shop in the market and people ask him where riba-based banks are; should he tell them?
It is haraam to deal with riba-based banks in order to get a loan or to put money in savings accounts, because that is riba and is haraam. It is also haraam to put money in current accounts except when that is necessary in order to protect the money when there is no Islamic bank.
There are other haraam transactions that are done by riba-based banks, having to do with letters of credit, credit cards, and so on.
It is permissible to deal with these banks with regard to permissible matters such as transferring money, exchanging currency, cashing cheques and so on.
Based on that, the person who asks you where the bank is may want to go there for a permissible purpose, in which case your telling him would not come under the heading of cooperating in sin and transgression.
If you want to be on the safe side and not tell anyone where the bank is under any circumstances, they you should use a double-entendre when replying, such as saying, It is close to here, or not far away, but ask someone who can describe it properly, and so on. You do not have to tell a blatant lie.
And Allah knows best.