Correct

毕竟 vs 究竟

/ bìjìng vs jiūjìng /
Strokes

Formula

1
问(一)个究竟
2
知道个究竟

Definition

毕竟 as an Adverb, which means [after all; in the final analysis];

究竟 as an Adverb or Noun, which means [after all; outcome].

Example

毕竟, means pointing out the crux but what follows will usually state admittedly the price one must pay or the understandable drawback.
1
Zhè
jìng
毕竟
shì
jìngzhēng
竞争
  
,
zǒng
yào
chū
付出
xīnxuè
心血
de
  

After all,it is a competition,and it is necessary for you to make efforts.

2
Xiǎowáng
小王
jìng
毕竟
hái
niánqīng
年轻
  
,
kǎo
考虑
wèn
问题
yǒushí
有时
qiàn
zhōudào
周到
  

After all,Xiao Wang is young and cannot take all factors into consideration.

3
Wángxiānsheng
王先生
jìng
毕竟
shì
wèi
shùxué
数学
jiā
  
,
luójiwéi
逻辑思维
néng
能力
hěn
jiàng
  

Mr.Wang is a mathematician,you know,and, naturally,his logical thinking is strong.

4
Kǎoshì
考试
jìng
毕竟
shì
kǎoshì
考试
  
,
zěn
néng
dāngr
  
儿戏
ne
  
!

After all, it is a test, how could you take it as a trifling matter?

毕竟, means "after all", implying something is hard-earned, long-awaited, etc.
5
Suīrán
虽然
fèi
le
hěnduō
很多
kǒushé
口舌
  
,
dàn
jìng
毕竟
míngbai
明白
le
zhège
这个
dàoli
道理
  

In the final analysis,he has understood the principle.

6
Suīrán
虽然
hái
yǒuxiē
有些
lěng
  
,
dàn
jìng
毕竟
shì
chūntiān
春天
le
  
,
tián
田野
kāishǐ
开始
yǒu
le
xiē
绿色
  

It is still a bit cold,but it is spring and the fields are covered with green.

究竟, as an adverb, means "after all" it and can be used in all sorts of questions to show the mood of further investigation.
究竟 in ① ② ③ cannot be replaced by 毕竟.
7
Zuò
zhè
jiàn
shìqing
事情
  
,
jiūjìng
究竟
yǒu
méiyǒu
没有
xìnxīn
信心
  
?

Frankly speaking,do you have confidence in it?

8
jiūjìng
究竟
shànghǎi
上海
háishi
还是
ān
西安
  
?

Where are you going actually, Shanghai or Xi'an?

9
Xuǎn
选择
le
zhème
这么
bàntiān
半天
  
,
jiūjìng
究竟
xiǎng
xué
shénme
什么
zhuān
专业
  
?

What major on earth does she want to study after thinking about it for a long time?

The usage of 究竟 is basically the same as 毕竟 (adv.) in above.

10
jiūjìng
究竟
  
(
jìng
毕竟
  
)
shì
mèimei
妹妹
  
,
yīnggāi
应该
duō
guānxīn
关心
  

Anyway, she is your sister,and you should take more care of her.

11
jiūjìng
究竟
  
(
jìng
毕竟
  
)
xué
guò
nián
huà
  
,
yǒu
xiē
一些
běngōng
基本功
  

After all, he learned painting for several years, so he has some basic skills.

究竟 as a Noun means "outcome or what actually happened".
问(一)个究竟 知道个究竟
12
Shìqing
事情
wèishénme
为什么
méi
bàn
chéng
  
,
xiǎng
zhīdào
知道
jiūjìng
究竟
  

He wants to know why the thing hasn't been done.