Which role makes it difficult for researchers to get information because they cannot ask questions that will around suspicion about themselves: ?

The answer is "Covert Participant".

In order to decrease the possibility for reactive results and to access the otherwise unreachable settings, various field researchers disguise and take part as covert participant where they keep their investigation secret and endeavor to gather as much as possible information in their covert role.

answer; dead end or culdesac;

semi-desert lowlands, hope this !