Well, if you're looking for automation of mod wheel in the arrangement view using the red automation line, because you'd like to automate it throughout your entire song (across many MIDI clips in the same track) and see it all the time as any other automation, that's a tricky one in Ableton.
Important thing to understand is, that mod wheel is MIDI CC message (CC #1). So it's recorded and also it's editable in the MIDI clip itself only (the same way as MIDI notes are - doubleclick on clip to see it in detail at the bottom part of the screen and there you can see/edit "envelopes". Mod wheel is one of that envelopes). So it's not automation, it's MIDI data.
BUT ...
How to see it in arrangement as red automation line in the track?
a) you'll get used to the said fact, that you have to record/edit mod wheel envelope inside every MIDI clip alone.
There's an option to "unlink" the envelope from the clip length so you'll be able to define it across more clips, but you still have to doubleclick the correct clip to edit it (not practical)
b) you'll make use of Ableton's routing and you'll create a separate MIDI track to define only mod wheel envelope across entire song and you'll also create track for MIDI notes (shorter clips / many separate clips as you're normally used to do an arrangement) and then you'll route these two MIDI tracks into third MIDI track where your VST/instrument actually is (this will effectively merge the MIDI messages together). Then you always know where the mod wheel envelope is and it will be "song wide". But you still have to doubleclick it to see it
c) if you have Max for Live, then great! This it totally doable. There's Max device called "CC map8":
https://maxforlive.com/library/device/2560/cc-map8
We can use this device to generate MIDI CC #1 (mod wheel) messages upon knob change. And we can automate this knob.
Just put this device before your VST/instrument, assign to one of the knobs the "CC #1" and move/automate the knob.
