首先,doubt 一般后面加that从句,他表述的是怀疑一个确定事实,而不是是不是第二,learn knowledge 是一个非常中文式的翻译其次,用lack太冗杂所以可以改为,i doubt that i am a student who only know how to learn without any observation.
后面用rather than是不是更好呢? rather than observe