keep on
Inseparable
Continue doing something, often repeatedly
He keeps on asking the same question.
Usage
Followed by '-ing': keep on trying.
Inseparable
The object always comes after the particle, even when it is a pronoun: look after the children, look after them.
Practise it
Add it to your daily practice or see every verb with on.
Further reading: keep on on Wiktionary (CC BY-SA).