adjusting x_axis_label or y_axis_label font/font size (Bokeh)

Figure exposes xaxis and yaxis attributes that you can use for that. In your use case it should be able to use:

p.xaxis.axis_label = 'whatever'
p.xaxis.axis_label_text_font_size = "40pt"

You can also adjust x and y labels simultaneously via the axis attribute:

p.axis.axis_label_text_font_style = 'bold'