Neither one of those. This statement is an example of the normal use of 'should', meaning 'Is it advisable for me to be working out?' or 'Am I supposed to be working out?" For example, a regular gym member who has a heart condition might ask this. You work out at the gym, but you are not sure whether this is a good thing or not - you are worried that you might be doing yourself harm by working out.

Possibility

Should is used to indicate that it will lead to the best outcome but you have a choice not to do it. It is used as an encouragement to get you to do it.

Please click the link below https://www.englishgrammar.org/showing-possibility/

The thing is you're now sure if you should work out or just have a rest. E.g. I'm not sure if I should be working out or having a rest.