How to get probability of classification
It is indeed a probability of 1 because you didn't change the default parameters. 

The probability for KNN is the average of all the neighbors. If there is only one neighbor n_neighbor=1 it can only be 1 or 0. 

The DecisionTreeClassifier expands until all the training data is classified perfectly if you don't control the depth. Again, this likely led to overfitting and to extreme probability predictions as a result. You should try different values for max_depth and see what works best. You can do say by performing cross validation. (If you are unfamiliar with these I recommend reading up on it first.)