Go on to ebay and buy a cheap obd2 scanner. Make sure its Vagcom compatible
This will do you
https://www.ebay.co.uk/itm/U281-VW-...672705&hash=item467016033d:g:TMwAAOSwHmhV8SON
OBD port on a golf is under the steering wheel closer to the door edge(youtube search your model)
Plug in with ignition on and run scan
It will find fault codes. Read fault codes and write them down
Abs sensors are very common failures on Golfs. Fault codes will look like 00283-00285 etc
This will tell you which part is failing.
After you have written down the fault codes erase the fault codes with your obd reader still connected. There is a chance that the ecu just needed wiping and there are actually no persistent faults. If the EML comes back on then you will need to replace the parts and wipe the fault codes again.
The ABS sensor is located in your wheel hub. You can buy aftermarket oem ones for about £10(ebay again)
They tend to break inside the hub so I usually have to drill them out, not as difficult as it sounds.
Anyway all of this is a common fix on golfs. If you do it yourself it will cost you less than £100 but if you are unsure of your mechanical skills ring around local independent garages, you will find one that can do the job for £200-£300.