In Weka, how to draw learning curve evaluated on both test and training set?
This is only possible with KnowledgeFlow. In WekaManual.pdf (which is included in Weka package) for version 3.7.12 there is an example in Chapter 7.4.2 "Plotting multiple ROC curves" with picture and step-by-step instructions. For other Weka versions it is the same, just find the appropriate chapter.

To give an impression on how it goes, I extracted the picture from the manual. It will draw two curves for two classifiers. For your question it is very similar. You use one classifier and then connect trainingSet to one ClassifierPerformanceEvaluator and testSet to another.