How long is a piece of string? *S*
Even very experienced riders have vastly differing degrees of mechanical knowledge. For some the idea of doing their own 'wrenching' rates right next to having a tooth pulled...for others the thought of letting anyone else near their beloved bike is devastating.
A basic working knowledge of your bike would suffice anywhere in Europe. Self-recovery knowledge such as puncture repair can come in handy anywhere. But basically it comes down to how much you have to spend.
Like anywhere else, being able to undertake basic servicings on your bike will save you much 'mulla' and is often more convenient as you can fit it in anywhere on your travel schedule. Anything more then tune ups etc would probably require more tools then you would have with you anyway...I'm yet to see anyone doing a top-end re-build on the side of the road *S*
Get a Workshop Manual for your intended bike, familiarise yourself with location and desired performance level of the basic components and you shoud be right.
If all else fails...you will find that a bike rider doesn't sit on the side of the road too long (at least in Europe, USA, Australia etc) before other riders will come along and give you a helping hand.
Finally, invest in a membership in a relevant Motorists Association that provides Roadside Assistance...just in case you ever find yourself stuck somewhere out of the way,
Good luck and all the Best,