The second sentence is fine.

The first isn't quite right. You could say  "My speaking skills are not very good but they're enough (for me) to get by (with) ".  'You' are the subject of the verb 'get by', so it's best if you are included in some way in that part of the sentence.

And can I say: My speaking skills are not very good but it is enough to get by.

                          My speaking skills are not very good but I can get by.

I haven't thought this through, so this is just my view:

The meaning is the same, but the preposition used depends on the object.

Get by 'on' is mainly used with quantifiable resources that can be 'spent'. For example "I can't get by on the money I earn" or "You can get by on 800 calories a day".

Get by 'with' is for other situations, for example, "If you're a tourist, you can get by with English, but if you're going to live there, it's better to learn the local language."