roguinrireki wo kakuninsi tara dou desu ka.

You’re right: normal Japanese is usually written without spaces.

The standard written form is:

ログイン履歴を確認したらどうですか。

Spaces are often added in teaching materials to make the grammar easier to see. Here they separate the sentence into chunks:

• ログイン履歴 = login history
• を = object marker
• 確認したら = if you check / how about checking
• どうですか = how is it? / how about it?

So the spaces are just a learning aid, not standard writing.

ログイン履歴 is a compound noun:

• ログイン = login, written in katakana because it is a loanword from English
• 履歴 = history / record / log, written in kanji

This kind of mix is very common in Japanese. Loanwords often stay in katakana, while more native or Sino-Japanese words are written in kanji.

So ログイン履歴 literally means something like login record or login history.

を marks the direct object of the verb.

Here, the verb is 確認する (to check / confirm), and the thing being checked is ログイン履歴.

So:

• ログイン履歴を確認する = to check the login history

In English, word order usually tells you what the object is. In Japanese, particles like を do that job.

This is because 確認する is being connected to another grammar pattern.

The full underlying form is:

確認する + たら

But when する is conjugated into the たら form, it becomes:

• する → した
• した + ら → したら

So:

• 確認する
• 確認したら

The し is just part of that conjugation process. It is not a separate word here.

〜たらどうですか is a very common pattern used to make a suggestion.

Structure:

• verb in たら form + どうですか

In this sentence:

• 確認したらどうですか

This means something like:

• How about checking it?
• Why don’t you check the login history?

It is softer than a direct command. Instead of telling someone what to do, it suggests an action.

This is a very common point of confusion.

Even though たら contains the た form, it does not always mean past time. In Japanese, 〜たら is also a conditional form meaning:

• if
• when
• after doing

In 〜たらどうですか, the pattern as a whole means How about doing ...?

So 確認したらどうですか is not saying How was it after you checked?
It is using the fixed suggestion pattern 〜たらどうですか.

Literally, yes, どうですか means how is it? or what do you think?

But in this grammar pattern, it works more naturally as part of a suggestion:

• 確認したらどうですか = How about checking it?
• 休んだらどうですか = Why don’t you take a rest?

So although the literal pieces are helpful to know, the sentence should be understood as a set expression for making suggestions.

It is polite, but also fairly soft and indirect.

• どうですか makes it polite
• 〜たらどうですか makes it sound like a suggestion rather than an order

Compared with other forms:

• ログイン履歴を確認してください。
  = Please check the login history.
  This is polite, but more direct.

• ログイン履歴を確認したらどうですか。
  = Why don’t you check the login history?
  This is softer and sounds more like advice.

So this sentence is often appropriate when you want to recommend something without sounding too forceful.

Yes, the subject is omitted, which is very normal in Japanese.

From context, the implied subject is usually you. So the sentence really means something like:

• Why don’t you check the login history?

Japanese often leaves out subjects when they are obvious from the situation. This is one of the biggest differences from English.

Yes. 〜てはどうですか is another common suggestion pattern.

So these are both possible:

• ログイン履歴を確認したらどうですか
• ログイン履歴を確認してはどうですか

They are similar in meaning:

• How about checking the login history?
• Why don’t you check the login history?

The nuance can vary a little depending on context, but for many learners, both can be understood as polite suggestions.

The dictionary form is 確認する.

This is a suru-verb, which means a noun plus する acts as a verb.

• 確認 = confirmation / checking
• 確認する = to confirm / to check

Some common forms are:

• 確認する = do/check/confirm
• 確認します = polite present/future
• 確認した = did check / checked
• 確認して = check and... / please check
• 確認したら = if/when you check

This sentence uses 確認したら, which comes from that same verb.

Yes, it sounds natural, especially in advice or support contexts.

For example, if someone says they think their account was accessed by someone else, replying with:

ログイン履歴を確認したらどうですか。

would sound like a natural suggestion: Why don’t you check your login history?

That said, in real conversation, people might also use shorter or slightly different versions depending on tone, such as:

• ログイン履歴を確認してみたらどうですか。
  = Why don’t you try checking the login history?

Adding 〜てみる makes it sound even more like a suggested step to try.

履歴 is read りれき.

So the whole phrase is read:

ログインりれき

And the full sentence is:

ログインりれきを かくにんしたら どうですか。

If you are reading aloud naturally, though, you would usually say it smoothly without pauses between every chunk.