What is the term for an exam which is conducted physically in an examination hall with all the students on the premises?

Solution 1:

In-person exam is the wording that comes to my mind. For example:

• States should postpone in-person bar exams during COVID-19 pandemic, ABA House says

• NJ In-Person Boating Exam

• All exams are computer based and will be completed in person at one of our test sites around Washington State. — Assessments for Grades 3–8 | Washington Virtual Academies

You can also use it as an adverb:

• The Board of Regents and Department's task was to create a framework to help guide schools and school districts as they continue to plan for school to return in the fall, whether instruction takes place in person, remotely, or through some combination of the two. — Reopening Schools Guidance - New York State Education

Solution 2:

Conducting a Google search for "examinations, whether online or" gives (among others) the following results:

• examinations[,] whether online or offline (often sources in India)
• examinations[,] whether online or face-to-face (not really appropriate for written exams)
• examinations[,] whether online or on paper (though even exams conducted in central venues may be non-paper)
• examinations[,] whether online or on-site (DU’s Sociology department)

I'd go with on-site, though offline is catching on.