As such we don't have any specific method to identify defects that haven't been touched.
ALM/QC just presents the data to users and does not mark/enter data into the record.
It is when the user actually adds or changes information (adds a note, changes a value in a drop-down) that way the record gets updated.
It has various filters like Status, Priority, Severity etc., based on those, we can identify the defects. We have field called ''last modified'' date/time
the field gets updated too and can be used to find recently ''updated'' records.

Also, refer the following link how to search for defects.
http://alm-help.saas.hpe.com/en/12.53/online_help/Content/UG/t_search_defects.htm

Regarding query, You can query specific data that is stored in your project or template project. You query a project by defining and running SQL queries. The following examples show SQL queries and the results that they return.

select * from BUG where BG_STATUS = 'Open' (All defects that are open.)
select * from BUG where BG_RESPONSIBLE = 'james_alm' or BG_RESPONSIBLE = 'mary_alm' (All defects assigned to either James or Mary.)
select count (*) from BUG where BG_RESPONSIBLE = 'mary_alm' (The number of defects assigned to Mary.)
select * from BUG where BG_RESPONSIBLE='james_alm' and BG_STATUS='open' (All open defects assigned to James.)
Hope this, resolves your question.

This SQL query can easily be run from Site Admin when expanding detail below project in Site Projects tree to see the list of tables.

In QC 11, there was also an ''Excel Report'' in the Analysis view that could be created with SQL. (today, 11.50 and later, you could enable that report with a system parameter -

http://eyeontesting.com/questions/14453/back-in-qc11-i-used-excel-report-now-i-dont-see-th.html?childToView=14454#answer-14454