The exported structure contains the model as one of the fields. This model field in turn contains all the parameters that would be otherwise found in the model output if the corresponding function was invoked. For example, if Regression Learner App is used and "Stepwise Linear Model" is chosen from the drop-down for Model Type, once the training is complete, the RMSE, R squared and other model parameters are displayed in the app. The model can be exported into a structure and its parameters, say for example, R squared can be accessed by:
>> RSquared = trainedModel.LinearModel.Rsquared.Ordinary;
Not all models will have all the parameters. For example, if you use an ensemble of bagged trees in the Classification Learner App, you will not get R squared value. If you are looking for a parameter that is not listed, please check the documentation to ensure it is generated for the type of model you are using.