Here is a translation of the sentence:
Reisen ist einer der attraktivsten Aspekte bei meiner Arbeit.
Travel is one of the most attractive aspects of my work.
This sentence has a really complicated grammatically structure, so let's answer your questions first and let's then have a closer look to the details.
- Is "Reisen" the subject?
Yes.
- Is "Aspekte" an object in accusative case?
No and no. (It's neither an object nor in accusative case)
- The ending of the adjective "attraktivsten" is -en. Is it because it is in accusative case or because it is in plural?
No, none of you assumptions is correct. It is a superlative.
- Why is it "einer"? Does it refer to "bei meiner Arbeit"?
No. This word means »one«, so it's a numeral and numerals do not refer to anything. (Pronouns refer to other things, but numerals and pronouns are different categories of words.) Numerals just count things. (Well, you could define counting as some kind of reference, but that's not what reference usually means in grammar.)
Now for the details:
When ever you have a verb that is a copula (i.e. a "coupling verb" like sein = to be; werden = to become, bleiben = to stay) then there is a high change, that you find two parts of speech in nominative case in the sentence. One is the subject, that exists in all sentences (with very rare exceptions) and the other is a so-called »Gleichsetzungsnominativ« (equative nominative). If this is the case, then the sentence expresses, that two things are equal. This is the case here, and the two equal things are:1
- Reisen = Travel
- einer der attraktivsten Aspekte = one of the most attractive aspects
The core of the equative nominative group is the numeral »einer« So this is already a grammatically correct and complete German sentence:
Reisen ist einer. (Travel is one.)
But it contains almost no information on the semantic level. So, you add an attribute to »einer«, and here we have another nominal group that is this attribute, but when a nominal group is an attribute of something else, then this group appears in genitive case. Here are some examples. Everything that is marked bold is a nominal group that is used as an attribute and it is in genitive case.:
Hier ist der Hut. → Hier ist der Hut meines Vaters.
Ganz oben auf der Speisekarte steht das Gericht. → Ganz oben auf der Speisekarte steht das Gericht des Tages.
Beim Überqueren fiel plötzlich der Motor aus. → Beim Überqueren des Ärmelkanals fiel plötzlich der Motor aus.
Einer stand plötzlich vor meiner Tür. → Einer der Soldaten stand plötzlich vor meiner Tür.
Such attributes are not grammatically necessary, but they often contain important information and may even be the most important part of a sentence from a semantic point of view.
The last examples show an often used pattern: One of many. You name a group in the genitive attribute, and the thing, of which this is the attribute, is just the word one or in German: eine, einer or eines. And there is always another way to express the same meaning, and this works also in English:
eines der Kinder = ein Kind
one of the children = one child
einer der Männer = ein Mann
one of the men = one man
eine der Frauen = eine Frau
one of the women = one woman
But when you use the version with the attribute, you emphasize, that the one is a part of many of the same kind:
- Here you are not mentioning any other aspects at all:
Reisen ist der attraktivste Aspekt bei meiner Arbeit.
Travel is the most attractive aspect of my work.
- Here you add, that there are also many other attractive aspects:
Reisen ist einer der attraktivsten Aspekte bei meiner Arbeit.
Travel is one of the most attractive aspects of my work.
The adjective attraktiv is a comparable adjective:
degree of comparison |
German |
English |
positive |
attraktiv |
attractive |
comparative |
attraktiver |
more attractive |
superlative |
(am) attraktivsten |
most attractive |
When you use the superlative form, you need the word am only in predicative and adverbial usage:
- predicative (connected to the subject by a copula verb):
Sabine ist am attraktivsten.
- adverbial (attribute of a verb):
Sabine lächelt am attraktivsten.
But when a superlative is used attributive, then you don't need »am«:
- attributive (attribute of a noun and together with that noun in the same nominal group):
Sabine ist die attraktivste Frau.
Berlin ist wieder das wirkliche Zentrum von Deutschland.
Has the adjective "wirklich" the ending -e, because "Zentrum" is consider as Object in accusative case?
No. Zentrum is not in accusative case, but again part of a Gleichsetzungsnominativ (equality nominative) and therefore in nominative case. So also the attributive adjective is inflected in nominative case.
Here are the five grammatical properties that influence the declension of adjectives:
- Comparison (positiv, comparativ or superlative?)
Here: positiv (no comparison)
- Definiteness or degree of declension
In German we have strong, weak and mixed declension of adjectives. This depends on whether there is an article or not, and if there is one, if its a definite article (like "the" in English) or an indefinite article (like "a" or "an" in English). Here we have the definite article »das«, and having a definite article means that you must use weak declension.
- Grammatical number (singular or plural)
Here we have: singular (only one Zentrum = center)
- Grammatical gender of the noun (masculine, feminine or neuter)
This category applies only if the number is singular. But this is the case here. So, we must know the gender of the noun »Zentrum«. It is neuter, and so also the adjective must be declined neuter.
- Grammatical case (nominative, genitive, dative or accusative)
We already found out the case: it is nominative.
And the nominative neuter singular weak positive declension of »wirklich« is:
wirkliche
1 The prepositional phrase »bei meiner Arbeit« is also interesting but not topic of your question. It is neither an object of the verb (copulas don't take objects (except for free dative objects)) nor an attribute of »einer« or »Aspekte«. It is an adverbial part of speech that provides a context for the whole sentence.