Here "understanding" refers to understanding about God. This can be stated clearly. AT: "as you learn and understand more about what pleases God" (See: [[rc://en/ta/man/translate/figs-explicit]])
The words "sincere" and "without offense" mean basically the same thing. Paul combines them to emphasize moral purity. AT: "completely blameless" (See: [[rc://en/ta/man/translate/figs-doublet]])
Being filled with something is a metaphor that represents being characterized by it or by habitually doing it. Possible meanings of "fruit of righteousness" are that 1) it is a metaphor that represents righteous behavior. AT: "you also will habitually do what is righteous because Jesus Christ enables you" or 2) it is a metaphor that represents good deeds as a result of being righteous. AT: "you also will habitually do good works because Jesus makes you righteous" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Possible meanings are 1) "Then other people will see how you honor God" or 2) "Then people will praise and give honor to God because of the good things they see you do." These alternate translations would require a new sentence.