What are the original Chinese characters for the Chinese family name Suening in the Philippines?
Chinese in Macau are mostly Cantonese speakers. It is not uncommon for people to write last name before the first name in Chinese speaking regions. 

In your grandfather case "Leo" would actually be the last name. According to British Romanization of Chinese characters "Leo" is most likely "廖" /liu6/ or 柳 /lau5/

Suening was most likely two characters written as one English word, that provided further evidence for 'Leo' (廖/柳) being the family name

Suening as  Sue-Ning make more sense than Suen-Ing because 'Ning'(寧) is a very common first name

The Chinese characters for 'Leo Sue Ning' could be 
廖信寧, 柳信寧, 廖迅寧, 柳迅寧, 廖迅齡 or 柳信齡 in Cantonese. 

廖/柳信寧 seems to be most probable

Edit:

Suening wrote:


  Hi, I got my Gedmatch (DNA) results and distant relative has 梁 from en.wikipedia.org/wiki/Liang_(surname) is it totally different from the given above? 


梁 in Hong Kong is written as 'Leung'.  "Leo" might be a pronunciation from a Cantonese sub-dialect for 梁. And it is a common surname.

Therefore, 'Leo Sue Ning' could be 

梁信寧, 梁迅寧 or 梁信齡

Edit 2:


  This turned a bit complicated as I leaned towards the 'Leong', more and more users were added with the names of 'Liu' (劉) - list; Liu Gui Hua, XiaoxueLiu, Liu Jin Lian, Liu Li Qun, Chang Liu, John Liu, Xiaoou Liu, Liu Shun Ying, Haoshu Liu, Ismayil Liu, Liu, Liu Su Hua, Liu Gui Hua, XiaoxueLiu, Liu Jin Lian


So it could be 劉信寧, 劉迅寧 or 劉信齡 then. Both 劉 and 梁 are very common Chinese surnames. It doesn't change the fact that 'Suening' was most likely  a two characters given name 'Sue Ning' mistakenly turned into a Surname in  the Philippine