Ask him/her to describe how SAP handles Memory Management?
ST02 / ST03 In general via table buffers, you could go into the whole Work Process, roll in, roll out, heap (private) memory, etc. however just as a Unix or DBA admin would know, is you look this up when needed for the exact specifics.
Ask him/her to describe where they would look at the buffer statistics, and what steps they would use to adjust them?
ST02, RZ10

Ask him/her to describe how to setup a printer in SAP or where they would look to research why a user/users can not print?
SPAD, SP01, SM50, SU01

Interview to 3 general areas:
DB (what is the directory structure/ where are the files kept oracle alerts, init.ora, redo logs, archive logs, etc.; possibly some basics stuff like what to do “high level” when the archive directory fills up, etc. Keep this minimal as from a SAP basis admin point of view Oracle is just a big giant bit bucket and SAP can handle to the daily monitoring and maintenance itself.
OS (what is the directory structure (what is NFS mounted and why / where are the message files contained for the OS error log; basic commands for the OS eg. Unix, mv, cp, ls, grep, ps-ef, df-k, etc. That is pretty much all the SAP basis admin will need to know. Client/Server architecture.
SAP (what is the directory structure / where are files located ie. profiles – start, instance, default (what are they and what is the order of precendence) start is for statup only, instance is the first to be read then the default and if a given parameter cannot be found in the instance or then the default then the internal standard is taken from RZ10 setting.
You can ask them to ran Transaction codes to you. Menus constanly change so go with T-codes. He should have a good knowledge of the following areas; transports, user / print / spool / batch management, monitoring, client tools and copies, support packages, kernel patches, workload analysis, Roles and Security, etc.
The standard list of t-codes is pretty much
SM50, SM51, SM66, SM12, SM13, SM21, DB01, DB02, DB13, ST01, ST02, ST03, ST04, ST05, ST06, SU01, SUIM, PFCG, SCC4, SE01, SE09, SE10, SPAM, SM35, SM36, SM37, SPAD, SP01 SCC3, SCCL, SCC9 this are pretty much you heavy hitters for monitoring and support.
I would ask in general how he would troubleshoot the following:
- User cannot connect to SAP
check SAP logon settings, ping the host, check message server, check dispatcher, etc.
- User cannot print
check SAP user setup, check SPAD, check spools, check unix queue or print queue at the os level, etc
- System seems slow
check SM66, SM51, SM50, SM21, ST06, ST03, SMLG, AL08 etc.
Some important things to remember is to ask not get specific to your installation or specific system setup as all SAP instances are different, keep your question to general topics and general answers.
The most important thing to notice when choosing a candidate is not how they parrot back answers to you, but if they can a) think for themselves and b) they actually like to and will keep on learning as no one knows it all and c) they have a good background and willingness to perform analyis and will keep on digginging until the answer is found or until their resources are exhausted and then they will pull in what is required to figure it out.