Is it more correct or appropriate to say:
"I have strong organisation skills" OR "I have strong organisational skills"?
'Organisation skills' might be interpreted as skills to work the particular organisation in which the person concerned operates. They would be an outstanding practitioner of the internal politics of that organisation.
By contrast, 'organisational skills' are the skills needed to organise something: a school sports day, or the D-day invasion of France in 1944.
So, both terms are grammatically correct, but they mean quite different things.