My father has been diagnosed with invasive moderately differentiating keratinising squamous cell carcinoma on his right cheek. is it curable

Likely yes: Provided the tumor is entirely removed, it may be cured. However, patients with sun exposure-related cancers are often susceptible to developing new cancers in sun-exposed skin, so he'll have to be closely followed by a dermatologist going forward, with vigorous use of sunscreen and other sun-protective means (hat, umbrella, etc) during prolonged exposure.