Determine how each feature contribute to XGBoost Classification
If you have just then parameters and two of them are important. You can plot the trees and see the threshold for each of the parameters. 

from xgboost import XGBClassifier
from xgboost import plot_tree
import matplotlib.pyplot as plt

# fit the model 
model = XGBClassifier().fit(X, y)
# plot single tree
plot_tree(model)
plt.show()



The above code just plots the first tree. You can plot, for example, 4th boosted tree in sequences using the following line of code

plot_tree(model, num_trees=3)


Note that in each tree, you might have a different threshold for each parameter in an ensembling method.