Сесе "passion for what you do is essential in any profession"said daniel humm. what do you think makes your future professional passionate? what will you do to keep passion alive in your profession after making career for many years? ​

1) Does his son know English well? Does his son know English or German well? What language does his son know well?   His son knows English well, doesn't he?
2) Do our parents grow wheat? Do our parents grow wheat or rice? What do our parents grow? Our parents grow wheat, don't they?
3) Did Peter see them in the park? Did Peter see them in the park or at school? Where did Peter see them? Peter saw them in the park, didn't he?
4) Will his parents be at home after six? Will his parents be at home after six or seven? When will his parents be at home? His parents will be at home after six, won't they?
5) Are they working in the garden? Are they working or relaxing in the garden? Where are they working? They are working in the garden, aren't they?

I like TO play.
Play - глагол, начальная форма, поэтому нужна частица TO
I like playing.
Playing - герундий

По поводу разницы:
I like reading = I enjoy in general
I don't like reading = I do but don't enjoy
I like to read in bed = there is a restriction
I like to go to a dentist = I find it wise/good/right
I don't like to read = I don't read

I like reading - Я люблю читать (чтение) , то есть мне нравится сам процесс. Употребляем герундий, когда говорим о хобби, интересах.
I like to read. - Люблю почитать. То есть я в принципе не против подобного действа, это неплохое занятие.