Qual è la differenza tra Sepenuhnya = Aku memahami sepenuhnya e Sepenuh = Aku mencintaimu sepenuh hati ?Sentiti libero di rispondere con un esempio.

@Zerkion sepenuhnya has root word "penuh" which literally means full. Hence:
- Sepenuhnya -> Fully (I understand fully)
- Sepenuh hati -> All my heart (I love you with all my heart). In fact, you can also say "Aku mencintaimu sepenuhnya", although it sounds less poetic of course.

Some other sentences using "sepenuh":
- Mereka memberikan sepenuh perhatian (they gives full attention).
=> Note: Most people will only say "segenap" here, but this is grammatically correct.
- Gelasnya mau diisi sepenuh apa? (how full would you like to fill-up the glass?)

From the example above, you can see, "sepenuhnya" does not followed by an object, whilst with only "sepenuh" you need to have an accompanying object.

The prefix se- combined with sufix -nya, can be used to make things superlative. Example:
- Sepenuh-penuhnya -> As full as possible.
=> Airnya mau sepenuh apa? Sepenuh-penuhnya aja (How full would you like the water be? As full as possible).
- Sepanas-panasnya -> As hot as possible.
=> Airnya mau sepanas apa? Sepanas-panasnya aja (How hot would you like the water be? As hot as possible).
- Sebesar-besarnya -> As big as possible.
=> Kertasnya mau sebesar apa? Sebesar-besarnya (How big would you like the paper be? As big as possible).
- Sebanyak-banyaknya -> As much as possible.
=> Mau duit berapa? Sebanyak-banyaknya :-D (How much money would you like? As much as possible :-D).

Hope this helps. Cheers.