指睇有冇文法錯

1. Your view on "collective memory."
沒有寫錯

2. How to balance between preservation and development.
這句單獨來說沒問題，但跟前文就有點兒不妥。Please share with us是向他人說分享心得，除非答話者是有故物保護和社區發展的經驗(how to)，你的問法就不正確。你或可以說：Your opinion on balancing between preservation and development.

3. Buildings or places in Hong Kong where it is memorable to you.
這句文法有問題，因為後段該是個relative clause，不會有"it is."若按照你用的語法，你可以寫成： Buildings or places in Hong Kong that are memorable to you.用較地道的英文，你可以把後句寫成... that you find memorable.

In this session, please present your ideas on
1.Your views on “Collective Memory"
2.How to balance preservation and development
3.Memorable places or buildings in Hong Kong

唔好用中文諗英文, 如果唔係文法會好怪

I think number 1 is ok.

but number 2, I will suggest you:
how to balance between the preservation (of something, eg, natural resources) and the development (of the city??)-- by doing that the question is clearer in terms what you are comparing.

number3:
buildings or places in Hong Kong THAT are memorable to you.

You should use the following will be better:

In this section, please share yourself with us:
1. Your view on “collective memory”.
2. How to balance preservation and development.
3. Buildings or places in Hong Kong where is memorable.