I am a “verse by verse, chapter by chapter, keep it in context” type when I study, but not everyone is. You may prefer topical study. For that, try using the concordance or subject index in the back of your Bible.
A concordance lists each occurrence of a key word in Scripture. Some ‘back of the Bible’ ones are more complete than others. If you want complete, try Strong’s, Young’s or Cruden’s.
Strong’s is very complete, exhaustive even and has become the standard. There are a few things that make it difficult to use. It is arranged by the Greek or Hebrew word, so you need to know those to look words up. Also, we read in English. The word hesed in Hebrew is translated lovingkindess, mercy, love and several other ways. Then there are other words translated mercy. If you wanted to study mercy, you’d need to know all those Hebrew or Greek words.
Young’s is arranged by the English word. If you looked up mercy, it would list all the occurrences original language words translated mercy. It’s more practical for people not wanting to get into Hebrew or Greek.
Cruden’s is based off the KJV, so if you’re not familiar with its wording, this one may not help much. I use it in situations where you know the words, but don’t know where they’re found. You know, something about mercies new every morning… Oh yeah. Lamentations 3:23.
A subject index covers a limited number of topics, so it is less complete but great for a quick study.
Topical Bibles are arranged similarly but are more complete.
A Bible Dictionary can also be a great tool for a topical study. Here’s the entry from the Holman Bible Dictionary for thanksgiving.THANKSGIVING 1. Gratitude directed towards God …, generally in response to God’s concrete acts in history. Thanksgiving was central to Old Testament worship. Sacrifice and offerings were to be made not grudgingly but with thanksgiving (Ps. 54:6; Jonah 2:9). The psalmist valued a song of thanksgiving more than sacrifice (Ps. 69:30-31). David employed Levites “to invoke, to thank, and to praise the Lord” (1 Chron. 16:4; also 23:30; Neh. 12:46). Pilgrimage to the Temple and Temple worship were characterized by thanksgiving (Pss. 42:4; 95:2; 100:4; 122:4). Thankfulness was expressed: for personal (Ps. 35:18) and national deliverance (Ps. 44:7-8); for God’s faithfulness to the covenant (Ps. 100:5); and for forgiveness (Ps. 30:4-5; Isa. 12:1). All creation joins in offering thanks to God (Ps. 145:10). See Psalms. Thanksgiving is a natural element of Christian worship (1 Cor. 14:16-17) and is to characterize all of Christian life (Col. 2:7; 4:2). Early Christians expressed thanks: for Christ’s healing ministry (Luke 17:16); for Christ’s deliverance of the believer from sin (Rom. 6:17-18; 7:25); for God’s indescribable gift of grace in Christ (2 Cor. 9:14-15; 1 Cor. 15:57; compare Rom. 1:21); and for the faith of fellow Christians (Rom. 1:8). 2. Epistolary thanksgiving: An element in the opening of a typical Greek letter. All of the Pauline Letters with the exception of Galatians begin with a thanksgiving. See Letters.
(Holman Bible Dictionary Copyright © 1991 Holman Bible Publishers. All rights reserved. International copyright secured.)