首先,更正一下提问中的错误: 没有forgetable这个词,其正确写法是forgettable。
因此，这个问题应更正为：forgetful与forgettable有何区别?
下面正式解答这个问题。
1.forgetful adj.（指人或形容人）健忘的; 易忘事的; 疏忽的。
She is a forgetful girl. 她是个健忘的女孩。（forgetful作定语）
My mother has become very forgetful and confused recently.
我妈妈近来变得非常健忘，糊里糊涂。（forgetful作表语）
来自柯林斯例句
Grandfather is forgetful and often repeats himself when he tells a story.
爷爷记忆不好，他讲故事时老爱重复。 （forgetful作表语）
来自《简明英汉词典》
Every actor ought to know his lines backwards before he goes on stage, as nervousness may
make him forgetful.
所有演员在上台前都应当把台词记得滚瓜烂熟, 因为一紧张就容易忘词。（forgetful作宾补）
来自《简明英汉词典》
以上例句中forgetful词义都是“健忘的;易忘事的;”。
The clerk was forgetful of his duties and was dismissed by the company.
该员工玩忽职守，被公司解雇了。（forgetful作表语,意为“疏忽的”。）
2.forgettable adj.(因平淡无奇)容易被遗忘的，不被人记住的; 可以忘记的。
指人或事物、事件等容易被人遗忘的、不被人记住的、不起眼的、可以忘记的。
He has a forgettable face. 他长着一张过目即忘的脸。
He has acted in three forgettable action films. 他曾经在三部不起眼的动作片中出演角色。
以上例句来自金山词霸
3.拓展延伸：
unforgettable adj.难忘的，令人难忘的，不能忘记的。
be forgetful of sb./sth. （对某人/某事物）不考虑、疏忽
be forgetful of one's duties 玩忽职守
be forgetful of one's sleep and meals 废寝忘食
A visit to the museum is an unforgettable experience.
参观博物馆是一段令人难忘的经历。（unforgettable 作定语）
来自柯林斯例句
The film is unforgettable because there are lots of wonderful fight scenes in it.
这部影片令人难忘，因为其中有许多精彩的武打场面。（unforgettable 作表语）
The scientist is so absorbed in his work that he is often forgetful of his sleep and meals.
那位科学家专心致志地工作，常常达到废寝忘食的程度。（forgetful作表语）